Use helper macros to define base::Features in //components/variations

This allows:
- features to be defined with a consistent set of qualifiers, and for
  that set of qualifiers to be updated over time as appropriate.
- better PRESUBMIT checks to ensure that base::Features are not defined
  in headers.
- simplifies things for scripts trying to extract feature definitions
  out of C++ code.

The primary CL was generated using a script that automatically rewrites
base::Feature declarations and definitions to the macro form. Changes to
any files with known incompatibilities with the macros (base::Features
without static storage duration and base::Features declared as static
class members) were then fully reverted; those changes will be manually
handled in followups.

This is an automated cleanup pass with manual fixups to add additional
static specifiers where needed.

Bug: 1364289
Change-Id: Ib5c625ec8150f115cc819819ecb478a20b12d7af
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3931194
Reviewed-by: Lei Zhang <thestig@chromium.org>
Auto-Submit: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Owners-Override: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1053881}

components/variations/variations_seed_processor_unittest.cc

@@ -500,15 +500,12 @@ TYPED_TEST(VariationsSeedProcessorTest, ForcingFlagAlreadyForced) {
 }
 
 TYPED_TEST(VariationsSeedProcessorTest, FeatureEnabledOrDisableByTrial) {
-  struct base::Feature kFeatureOffByDefault {
-    "kOff", base::FEATURE_DISABLED_BY_DEFAULT
-  };
-  struct base::Feature kFeatureOnByDefault {
-    "kOn", base::FEATURE_ENABLED_BY_DEFAULT
-  };
-  struct base::Feature kUnrelatedFeature {
-    "kUnrelated", base::FEATURE_DISABLED_BY_DEFAULT
-  };
+  static BASE_FEATURE(kFeatureOffByDefault, "kOff",
+                      base::FEATURE_DISABLED_BY_DEFAULT);
+  static BASE_FEATURE(kFeatureOnByDefault, "kOn",
+                      base::FEATURE_ENABLED_BY_DEFAULT);
+  static BASE_FEATURE(kUnrelatedFeature, "kUnrelated",
+                      base::FEATURE_DISABLED_BY_DEFAULT);
 
   struct {
     const char* enable_feature;
@@ -571,12 +568,10 @@ TYPED_TEST(VariationsSeedProcessorTest, FeatureEnabledOrDisableByTrial) {
 }
 
 TYPED_TEST(VariationsSeedProcessorTest, FeatureAssociationAndForcing) {
-  struct base::Feature kFeatureOffByDefault {
-    "kFeatureOffByDefault", base::FEATURE_DISABLED_BY_DEFAULT
-  };
-  struct base::Feature kFeatureOnByDefault {
-    "kFeatureOnByDefault", base::FEATURE_ENABLED_BY_DEFAULT
-  };
+  static BASE_FEATURE(kFeatureOffByDefault, "kFeatureOffByDefault",
+                      base::FEATURE_DISABLED_BY_DEFAULT);
+  static BASE_FEATURE(kFeatureOnByDefault, "kFeatureOnByDefault",
+                      base::FEATURE_ENABLED_BY_DEFAULT);
 
   enum OneHundredPercentGroup {
     DEFAULT_GROUP,
@@ -1183,9 +1178,8 @@ TYPED_TEST(VariationsSeedProcessorTest, StudyWithLowerEntropyThanLayer) {
 }
 
 TYPED_TEST(VariationsSeedProcessorTest, StudiesWithOverlappingEnabledFeatures) {
-  static struct base::Feature kFeature {
-    "FeatureName", base::FEATURE_ENABLED_BY_DEFAULT
-  };
+  static BASE_FEATURE(kFeature, "FeatureName",
+                      base::FEATURE_ENABLED_BY_DEFAULT);
 
   VariationsSeed seed;
 
@@ -1225,9 +1219,8 @@ TYPED_TEST(VariationsSeedProcessorTest, StudiesWithOverlappingEnabledFeatures) {
 
 TYPED_TEST(VariationsSeedProcessorTest,
            StudiesWithOverlappingDisabledFeatures) {
-  static struct base::Feature kFeature {
-    "FeatureName", base::FEATURE_ENABLED_BY_DEFAULT
-  };
+  static BASE_FEATURE(kFeature, "FeatureName",
+                      base::FEATURE_ENABLED_BY_DEFAULT);
 
   VariationsSeed seed;