Revert "Disable COM Initialization on SchedulerWorkers When COM_INIT_CHECK_HOOK_ENABLED()"

This reverts commit 06f34ffd.

Reason for revert: Seems to have caused a test failure: https://luci-logdog.appspot.com/v/?s=chromium%2Fbb%2Fchromium.win%2FWin7_Tests__dbg__1_%2F61641%2F%2B%2Frecipes%2Fsteps%2Fbrowser_tests%2F0%2Flogs%2FPDFExtensionTest.DisablePlugin%2F0 in https://uberchromegw.corp.google.com/i/chromium.win/builders/Win7%20Tests%20%28dbg%29%281%29/builds/61641

Original change's description:
> Disable COM Initialization on SchedulerWorkers When COM_INIT_CHECK_HOOK_ENABLED()
> 
> This change will allow for the detection of tasks running in
> TaskScheduler that fail to post their task in a COM STA Task Runner
> instead.
> 
> BUG=706512
> 
> Change-Id: If8ea9df63cface0dc48aa11b5254ab3e6d87dc4f
> Reviewed-on: https://chromium-review.googlesource.com/549223
> Commit-Queue: Robert Liao <robliao@chromium.org>
> Reviewed-by: Gabriel Charette <gab@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#487269}

TBR=gab@chromium.org,robliao@chromium.org

Change-Id: Ie490ffab894364493a8b79fdb517e360d36ea4ee
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 706512
Reviewed-on: https://chromium-review.googlesource.com/574894Reviewed-by: Alice Boxhall <aboxhall@chromium.org>
Commit-Queue: Alice Boxhall <aboxhall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#487330}

base/task_scheduler/scheduler_worker.cc

@@ -15,7 +15,6 @@
 #if defined(OS_MACOSX)
 #include "base/mac/scoped_nsautorelease_pool.h"
 #elif defined(OS_WIN)
-#include "base/win/com_init_check_hook.h"
 #include "base/win/scoped_com_initializer.h"
 #endif
 
@@ -44,10 +43,7 @@ class SchedulerWorker::Thread : public PlatformThread::Delegate {
     // A SchedulerWorker starts out waiting for work.
     outer_->delegate_->WaitForWork(&wake_up_event_);
 
-    // When defined(COM_INIT_CHECK_HOOK_ENABLED), ignore
-    // SchedulerBackwardCompatibility::INIT_COM_STA to find incorrect uses of
-    // COM that should be running in a COM STA Task Runner.
-#if defined(OS_WIN) && !defined(COM_INIT_CHECK_HOOK_ENABLED)
+#if defined(OS_WIN)
     std::unique_ptr<win::ScopedCOMInitializer> com_initializer;
     if (outer_->backward_compatibility_ ==
         SchedulerBackwardCompatibility::INIT_COM_STA) {

base/task_scheduler/scheduler_worker_unittest.cc

@@ -30,8 +30,6 @@
 
 #if defined(OS_WIN)
 #include <objbase.h>
-
-#include "base/win/com_init_check_hook.h"
 #endif
 
 using testing::_;
@@ -933,13 +931,7 @@ TEST(TaskSchedulerWorkerTest, BackwardCompatibilityEnabled) {
 
   // The call to CoInitializeEx() should have returned S_FALSE to indicate that
   // the COM library was already initialized on the thread.
-  // See SchedulerWorker::Thread::ThreadMain for why we expect two different
-  // results here.
-#if defined(COM_INIT_CHECK_HOOK_ENABLED)
-  EXPECT_EQ(S_OK, delegate_raw->coinitialize_hresult());
-#else
   EXPECT_EQ(S_FALSE, delegate_raw->coinitialize_hresult());
-#endif
 
   worker->JoinForTesting();
 }