win7dep: Remove Win7+8 code in base/threading+task

Removes Win7 and Win8 specific code in base/task, getting rid
of Win7-specifc call to ScopedCOMInitializer.

Removes win7-specific thread priorities in base/threading,
and reworks description of SetThreadPriority kernel bug to describe
Win10+-only. Also removes test code for Win7.

Also fixes lint warning.

Bug: 1385856
Change-Id: I6d61ef5933cb61a4f0e17793fa06ef81ac0311b1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4113990
Reviewed-by: Francois Pierre Doray <fdoray@chromium.org>
Commit-Queue: David Bienvenu <davidbienvenu@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1084727}

base/task/thread_pool/thread_group.cc

@@ -17,9 +17,7 @@
 
 #if BUILDFLAG(IS_WIN)
 #include "base/win/com_init_check_hook.h"
-#include "base/win/scoped_com_initializer.h"
 #include "base/win/scoped_winrt_initializer.h"
-#include "base/win/windows_version.h"
 #endif
 
 namespace base {
@@ -327,18 +325,8 @@ bool ThreadGroup::ShouldYield(TaskSourceSortKey sort_key) {
 std::unique_ptr<win::ScopedWindowsThreadEnvironment>
 ThreadGroup::GetScopedWindowsThreadEnvironment(WorkerEnvironment environment) {
   std::unique_ptr<win::ScopedWindowsThreadEnvironment> scoped_environment;
-  switch (environment) {
-    case WorkerEnvironment::COM_MTA: {
-      if (win::GetVersion() >= win::Version::WIN8) {
-        scoped_environment = std::make_unique<win::ScopedWinrtInitializer>();
-      } else {
-        scoped_environment = std::make_unique<win::ScopedCOMInitializer>(
-            win::ScopedCOMInitializer::kMTA);
-      }
-      break;
-    }
-    default:
-      break;
+  if (environment == WorkerEnvironment::COM_MTA) {
+    scoped_environment = std::make_unique<win::ScopedWinrtInitializer>();
   }
 
   DCHECK(!scoped_environment || scoped_environment->Succeeded());

base/threading/platform_thread_win.cc

@@ -6,6 +6,8 @@
 
 #include <stddef.h>
 
+#include <string>
+
 #include "base/allocator/buildflags.h"
 #include "base/allocator/partition_allocator/partition_alloc_buildflags.h"
 #include "base/debug/activity_tracker.h"
@@ -47,14 +49,6 @@ namespace {
 // |kUseThreadPriorityLowest| Feature.
 std::atomic<bool> g_use_thread_priority_lowest{false};
 
-// The most common value returned by ::GetThreadPriority() after background
-// thread mode is enabled on Windows 7.
-constexpr int kWin7BackgroundThreadModePriority = 4;
-
-// Value sometimes returned by ::GetThreadPriority() after thread priority is
-// set to normal on Windows 7.
-constexpr int kWin7NormalPriority = 3;
-
 // These values are sometimes returned by ::GetThreadPriority().
 constexpr int kWinNormalPriority1 = 5;
 constexpr int kWinNormalPriority2 = 6;
@@ -237,10 +231,7 @@ void AssertMemoryPriority(HANDLE thread, int memory_priority) {
       reinterpret_cast<decltype(&::GetThreadInformation)>(::GetProcAddress(
           ::GetModuleHandle(L"Kernel32.dll"), "GetThreadInformation"));
 
-  if (!get_thread_information_fn) {
-    DCHECK_EQ(win::GetVersion(), win::Version::WIN7);
-    return;
-  }
+  DCHECK(get_thread_information_fn);
 
   MEMORY_PRIORITY_INFORMATION memory_priority_information = {};
   DCHECK(get_thread_information_fn(thread, ::ThreadMemoryPriority,
@@ -542,14 +533,8 @@ ThreadPriorityForTest PlatformThread::GetCurrentThreadPriorityForTest() {
     return ThreadPriorityForTest::kBackground;
 
   switch (priority) {
-    case kWin7BackgroundThreadModePriority:
-      DCHECK_EQ(win::GetVersion(), win::Version::WIN7);
-      return ThreadPriorityForTest::kBackground;
     case THREAD_PRIORITY_BELOW_NORMAL:
       return ThreadPriorityForTest::kUtility;
-    case kWin7NormalPriority:
-      DCHECK_EQ(win::GetVersion(), win::Version::WIN7);
-      [[fallthrough]];
     case THREAD_PRIORITY_NORMAL:
       return ThreadPriorityForTest::kNormal;
     case kWinNormalPriority1:

base/threading/platform_thread_win_unittest.cc

@@ -17,9 +17,8 @@ namespace base {
 
 // It has been observed that calling
 // :SetThreadPriority(THREAD_MODE_BACKGROUND_BEGIN) in an IDLE_PRIORITY_CLASS
-// process doesn't always affect the return value of ::GetThreadPriority() or
-// the base priority reported in Process Explorer (on Win7, the values are
-// sometimes affected while on Win8+ they are never affected). It does however
+// process never affects the return value of ::GetThreadPriority() or
+// the base priority reported in Process Explorer. It does however
 // set the memory and I/O priorities to very low. This test confirms that
 // behavior which we suspect is a Windows kernel bug. If this test starts
 // failing, the mitigation for https://crbug.com/901483 in
@@ -50,24 +49,15 @@ TEST(PlatformThreadWinTest, SetBackgroundThreadModeFailsInIdlePriorityProcess) {
   // Begin thread mode background.
   EXPECT_TRUE(::SetThreadPriority(thread_handle, THREAD_MODE_BACKGROUND_BEGIN));
 
-  // On Win8, GetThreadPriority() stays NORMAL. On Win7, it can stay NORMAL or
-  // switch to one of the various priorities that are observed after entering
-  // thread mode background in a NORMAL_PRIORITY_CLASS process. On all Windows
-  // versions, memory priority becomes VERY_LOW.
+  // On Win10+, GetThreadPriority() stays NORMAL and memory priority becomes
+  // VERY_LOW.
   //
   // Note: this documents the aforementioned kernel bug. Ideally this would
   // *not* be the case.
   const int priority_after_thread_mode_background_begin =
       ::GetThreadPriority(thread_handle);
-  if (win::GetVersion() == win::Version::WIN7) {
-    const ThreadPriorityForTest priority =
-        PlatformThread::GetCurrentThreadPriorityForTest();
-    EXPECT_TRUE(priority == ThreadPriorityForTest::kNormal ||
-                priority == ThreadPriorityForTest::kBackground);
-  } else {
-    EXPECT_EQ(priority_after_thread_mode_background_begin,
-              THREAD_PRIORITY_NORMAL);
-  }
+  EXPECT_EQ(priority_after_thread_mode_background_begin,
+            THREAD_PRIORITY_NORMAL);
   internal::AssertMemoryPriority(thread_handle, MEMORY_PRIORITY_VERY_LOW);
 
   PlatformThread::Sleep(base::Seconds(1));