Add a build version param to the ReduceUserAgentMinorVersion feature

The FeatureParam will allow setting the value of the frozen build number
in the Finch configuration.  If the param is set to X in the Finch
configuration, then the minor version would be 0.X.0.  The default value
is "0".

(cherry picked from commit 1356aec)

Bug: 1317577
Change-Id: I0bbd92031b916e6e372c36b9869634113b7fceff
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3594880
Reviewed-by: Mike Taylor <miketaylr@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Ali Beyad <abeyad@chromium.org>
Cr-Original-Commit-Position: refs/heads/main@{#994735}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3611532
Cr-Commit-Position: refs/branch-heads/5005@{#366}
Cr-Branched-From: 5b4d945-refs/heads/main@{#992738}

chrome/browser/chrome_worker_browsertest.cc

@@ -257,14 +257,23 @@ class ChromeWorkerUserAgentBrowserTest
         "Chrome/[0-9]+\\.([0-9]+\\.[0-9]+\\.[0-9]+)";
     // The minor version in the reduced UA string is always "0.0.0".
     static constexpr char kReducedMinorVersion[] = "0.0.0";
+    // The minor version in the ReduceUserAgentMinorVersion experiment is always
+    // "0.X.0", where X is the frozen build version.
+    const std::string kReduceUserAgentMinorVersion =
+        "0." +
+        std::string(
+            blink::features::kUserAgentFrozenBuildVersion.Get().data()) +
+        ".0";
 
     std::string minor_version;
     EXPECT_TRUE(re2::RE2::PartialMatch(user_agent_value, kChromeVersionRegex,
                                        &minor_version));
-    if (expected_user_agent_reduced ||
-        base::FeatureList::IsEnabled(
-            blink::features::kReduceUserAgentMinorVersion)) {
+
+    if (expected_user_agent_reduced) {
       EXPECT_EQ(minor_version, kReducedMinorVersion);
+    } else if (base::FeatureList::IsEnabled(
+                   blink::features::kReduceUserAgentMinorVersion)) {
+      EXPECT_EQ(minor_version, kReduceUserAgentMinorVersion);
     } else {
       EXPECT_NE(minor_version, kReducedMinorVersion);
     }

chrome/browser/client_hints/client_hints_browsertest.cc

@@ -247,14 +247,22 @@ void CheckUserAgentMinorVersion(const std::string& user_agent_value,
       "Chrome/[0-9]+\\.([0-9]+\\.[0-9]+\\.[0-9]+)";
   // The minor version in the reduced UA string is always "0.0.0".
   static constexpr char kReducedMinorVersion[] = "0.0.0";
+  // The minor version in the ReduceUserAgentMinorVersion experiment is always
+  // "0.X.0", where X is the frozen build version.
+  const std::string kReduceUserAgentMinorVersion =
+      "0." +
+      std::string(blink::features::kUserAgentFrozenBuildVersion.Get().data()) +
+      ".0";
 
   std::string minor_version;
   EXPECT_TRUE(re2::RE2::PartialMatch(user_agent_value, kChromeVersionRegex,
                                      &minor_version));
-  if (expected_user_agent_reduced ||
-      base::FeatureList::IsEnabled(
-          blink::features::kReduceUserAgentMinorVersion)) {
+
+  if (expected_user_agent_reduced) {
     EXPECT_EQ(minor_version, kReducedMinorVersion);
+  } else if (base::FeatureList::IsEnabled(
+                 blink::features::kReduceUserAgentMinorVersion)) {
+    EXPECT_EQ(minor_version, kReduceUserAgentMinorVersion);
   } else {
     EXPECT_NE(minor_version, kReducedMinorVersion);
   }

components/embedder_support/user_agent_utils.cc

@@ -341,7 +341,8 @@ std::string GetProductAndVersion(
   } else {
     if (base::FeatureList::IsEnabled(
             blink::features::kReduceUserAgentMinorVersion)) {
-      return version_info::GetProductNameAndVersionForReducedUserAgent();
+      return version_info::GetProductNameAndVersionForReducedUserAgent(
+          blink::features::kUserAgentFrozenBuildVersion.Get().data());
     } else {
       return version_info::GetProductNameAndVersionForUserAgent();
     }

components/embedder_support/user_agent_utils_unittest.cc

@@ -919,21 +919,38 @@ TEST_F(UserAgentUtilsTest, GetProductAndVersion) {
   EXPECT_EQ(major_version, "99");
   EXPECT_EQ(minor_version, version_info::GetMajorVersionNumber());
 
+  // Ensure the build version FeatureParam is used when set.
+  scoped_feature_list.Reset();
+  scoped_feature_list.InitWithFeaturesAndParameters(
+      /*enabled_features=*/{{blink::features::kReduceUserAgentMinorVersion,
+                             {{{"build_version", "5555"}}}}},
+      /*disabled_features=*/{
+          blink::features::kForceMajorVersionInMinorPositionInUserAgent});
+  product = GetProductAndVersion();
+  std::string build_version;
+  std::string patch_version;
+  EXPECT_TRUE(re2::RE2::FullMatch(product, kChromeProductVersionRegex,
+                                  &major_version, &minor_version,
+                                  &build_version, &patch_version));
+  EXPECT_EQ(major_version, version_info::GetMajorVersionNumber());
+  EXPECT_EQ(minor_version, "0");
+  EXPECT_EQ(build_version, "5555");
+  EXPECT_EQ(patch_version, "0");
+
   // Ensure policy is respected if ForcemajorToMinor is force disabled, even if
   // the respective Blink feature is enabled.
   scoped_feature_list.Reset();
   scoped_feature_list.InitWithFeatures(
       /*enabled_features=*/{blink::features::
                                 kForceMajorVersionInMinorPositionInUserAgent},
       /*disabled_features=*/{blink::features::kReduceUserAgentMinorVersion});
-  std::string build_version;
   product = GetProductAndVersion(/*force_major_to_minor=*/kForceDisabled);
   EXPECT_TRUE(re2::RE2::FullMatch(product, kChromeProductVersionRegex,
                                   &major_version, &minor_version,
                                   &build_version));
   EXPECT_EQ(major_version, version_info::GetMajorVersionNumber());
   EXPECT_EQ(minor_version, "0");
-  EXPECT_NE(build_version, "0");
+  EXPECT_NE(build_version, "9999");
 
   product = GetProductAndVersion();
   EXPECT_TRUE(re2::RE2::FullMatch(product, kChromeProductVersionRegex,
@@ -949,7 +966,6 @@ TEST_F(UserAgentUtilsTest, GetProductAndVersion) {
       /*disabled_features=*/{
           blink::features::kForceMajorVersionInMinorPositionInUserAgent});
   product = GetProductAndVersion();
-  std::string patch_version;
   EXPECT_TRUE(re2::RE2::FullMatch(product, kChromeProductVersionRegex,
                                   &major_version, &minor_version,
                                   &build_version, &patch_version));

components/version_info/version_info.cc

@@ -8,6 +8,7 @@
 #include "base/no_destructor.h"
 #include "base/notreached.h"
 #include "base/sanitizer_buildflags.h"
+#include "base/strings/strcat.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/version.h"
 #include "build/branding_buildflags.h"
@@ -23,10 +24,12 @@ const std::string& GetProductNameAndVersionForUserAgent() {
   return *product_and_version;
 }
 
-const std::string& GetProductNameAndVersionForReducedUserAgent() {
-  static const base::NoDestructor<std::string> product_and_version(
-      "Chrome/" + GetMajorVersionNumber() + ".0.0.0");
-  return *product_and_version;
+const std::string GetProductNameAndVersionForReducedUserAgent(
+    const std::string& build_version) {
+  std::string product_and_version;
+  base::StrAppend(&product_and_version, {"Chrome/", GetMajorVersionNumber(),
+                                         ".0.", build_version, ".0"});
+  return product_and_version;
 }
 
 std::string GetProductName() {

components/version_info/version_info.h

@@ -20,8 +20,10 @@ namespace version_info {
 const std::string& GetProductNameAndVersionForUserAgent();
 
 // Returns the product name and reduced version information for the User-Agent
-// header, in the format: Chrome/<major_version>.0.0.0.
-const std::string& GetProductNameAndVersionForReducedUserAgent();
+// header, in the format: Chrome/<major_version>.0.build_version.0, where
+// `build_version` is a frozen BUILD number.
+const std::string GetProductNameAndVersionForReducedUserAgent(
+    const std::string& build_version);
 
 // Returns the product name, e.g. "Chromium" or "Google Chrome".
 std::string GetProductName();

testing/variations/fieldtrial_testing_config.json

@@ -6279,6 +6279,9 @@
             "experiments": [
                 {
                     "name": "Enabled",
+                    "params": {
+                        "build_version": "9999"
+                    },
                     "enable_features": [
                         "ReduceUserAgentMinorVersion"
                     ]

third_party/blink/common/features.cc

@@ -1375,6 +1375,8 @@ const base::Feature kOptimizeViewportConstrainedPaintInvalidation{
 
 const base::Feature kReduceUserAgentMinorVersion{
     "ReduceUserAgentMinorVersion", base::FEATURE_DISABLED_BY_DEFAULT};
+const base::FeatureParam<std::string> kUserAgentFrozenBuildVersion{
+    &kReduceUserAgentMinorVersion, "build_version", "0"};
 
 const base::Feature kReportFCPOnlyOnSuccessfulCommit{
     "ReportFCPOnlyOnSuccessfulCommit", base::FEATURE_DISABLED_BY_DEFAULT};

third_party/blink/public/common/features.h

@@ -677,6 +677,8 @@ BLINK_COMMON_EXPORT extern const base::Feature
 
 // If enabled, the minor version of the User-Agent string will be reduced.
 BLINK_COMMON_EXPORT extern const base::Feature kReduceUserAgentMinorVersion;
+BLINK_COMMON_EXPORT extern const base::FeatureParam<std::string>
+    kUserAgentFrozenBuildVersion;
 
 // If enabled, we only report FCP if there’s a successful commit to the
 // compositor. Otherwise, FCP may be reported if first BeginMainFrame results in