Move around FieldTrial initialization in content:

. Content moves loading from PreCreateThreads() to
  PreEarlyInitialization() (or right after calling
  BrowserMainParts::PreEarlyInitialization()
  . This necessitated a change for cast to have content not init
    FieldTrials.
. Moves creation of FieldTrial in tests from
  TestBlinkWebUnitTestSupport to UnittestTestSuite. This is so code
  run after that (but before TestBlinkWebUnitTestSupport) has the
  FeatureList setup.

BUG=800357
TEST=none

Change-Id: I50e121f4c5654288571715b0e72bf04db340daf1
Reviewed-on: https://chromium-review.googlesource.com/925685Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#537817}

chrome/browser/chrome_browser_main.cc

@@ -1072,6 +1072,11 @@ DLLEXPORT void __cdecl RelaunchChromeBrowserWithNewCommandLineIfNeeded() {
 
 // content::BrowserMainParts implementation ------------------------------------
 
+bool ChromeBrowserMainParts::ShouldContentCreateFeatureList() {
+  // Chrome creates the FeatureList, so no need for content to do the same.
+  return false;
+}
+
 int ChromeBrowserMainParts::PreEarlyInitialization() {
   TRACE_EVENT0("startup", "ChromeBrowserMainParts::PreEarlyInitialization");
   for (size_t i = 0; i < chrome_extra_parts_.size(); ++i)

chrome/browser/chrome_browser_main.h

@@ -63,6 +63,7 @@ class ChromeBrowserMainParts : public content::BrowserMainParts {
       const content::MainFunctionParams& parameters);
 
   // content::BrowserMainParts overrides.
+  bool ShouldContentCreateFeatureList() override;
   // These are called in-order by content::BrowserMainLoop.
   // Each stage calls the same stages in any ChromeBrowserMainExtraParts added
   // with AddParts() from ChromeContentBrowserClient::CreateBrowserMainParts.

chromecast/browser/cast_browser_main_parts.cc

@@ -356,6 +356,10 @@ content::BrowserContext* CastBrowserMainParts::browser_context() {
   return cast_browser_process_->browser_context();
 }
 
+bool CastBrowserMainParts::ShouldContentCreateFeatureList() {
+  return false;
+}
+
 void CastBrowserMainParts::PreMainMessageLoopStart() {
   // GroupedHistograms needs to be initialized before any threads are created
   // to prevent race conditions between calls to Preregister and those threads

chromecast/browser/cast_browser_main_parts.h

@@ -72,6 +72,7 @@ class CastBrowserMainParts : public content::BrowserMainParts {
   content::BrowserContext* browser_context();
 
   // content::BrowserMainParts implementation:
+  bool ShouldContentCreateFeatureList() override;
   void PreMainMessageLoopStart() override;
   void PostMainMessageLoopStart() override;
   void ToolkitInitialized() override;

content/browser/browser_main_loop.cc

@@ -668,6 +668,16 @@ int BrowserMainLoop::EarlyInitialization() {
       return pre_early_init_error_code;
   }
 
+  if (!parts_ || parts_->ShouldContentCreateFeatureList()) {
+    // Note that we do not initialize a new FeatureList when calling this for
+    // the second time.
+    const base::CommandLine* command_line =
+        base::CommandLine::ForCurrentProcess();
+    base::FeatureList::InitializeInstance(
+        command_line->GetSwitchValueASCII(switches::kEnableFeatures),
+        command_line->GetSwitchValueASCII(switches::kDisableFeatures));
+  }
+
 #if defined(OS_MACOSX) || defined(OS_LINUX) || defined(OS_CHROMEOS)
   // We use quite a few file descriptors for our IPC as well as disk the disk
   // cache,and the default limit on the Mac is low (256), so bump it up.
@@ -862,14 +872,6 @@ int BrowserMainLoop::PreCreateThreads() {
   if (!base::SequencedWorkerPool::IsEnabled())
     base::SequencedWorkerPool::EnableForProcess();
 
-  const base::CommandLine* command_line =
-      base::CommandLine::ForCurrentProcess();
-  // Note that we do not initialize a new FeatureList when calling this for
-  // the second time.
-  base::FeatureList::InitializeInstance(
-      command_line->GetSwitchValueASCII(switches::kEnableFeatures),
-      command_line->GetSwitchValueASCII(switches::kDisableFeatures));
-
   InitializeMemoryManagementComponent();
 
 #if defined(OS_MACOSX)

content/public/browser/browser_main_parts.cc

@@ -8,6 +8,10 @@
 
 namespace content {
 
+bool BrowserMainParts::ShouldContentCreateFeatureList() {
+  return true;
+}
+
 int BrowserMainParts::PreEarlyInitialization() {
   return RESULT_CODE_NORMAL_EXIT;
 }

content/public/browser/browser_main_parts.h

@@ -53,6 +53,11 @@ class CONTENT_EXPORT BrowserMainParts {
   BrowserMainParts() {}
   virtual ~BrowserMainParts() {}
 
+  // Returns true if content should create a FeatureList. Default
+  // implementation returns true. Embedders that need to control when and/or
+  // how FeatureList should be created should override and return false.
+  virtual bool ShouldContentCreateFeatureList();
+
   // A return value other than RESULT_CODE_NORMAL_EXIT indicates error and is
   // used as the exit status.
   virtual int PreEarlyInitialization();

content/public/test/unittest_test_suite.cc

@@ -4,6 +4,7 @@
 
 #include "content/public/test/unittest_test_suite.h"
 
+#include "base/base_switches.h"
 #include "base/command_line.h"
 #include "base/logging.h"
 #include "base/rand_util.h"
@@ -24,6 +25,14 @@ namespace content {
 
 UnitTestTestSuite::UnitTestTestSuite(base::TestSuite* test_suite)
     : test_suite_(test_suite) {
+  const base::CommandLine* command_line =
+      base::CommandLine::ForCurrentProcess();
+  std::string enabled =
+      command_line->GetSwitchValueASCII(switches::kEnableFeatures);
+  std::string disabled =
+      command_line->GetSwitchValueASCII(switches::kDisableFeatures);
+  feature_list_.InitFromCommandLine(enabled, disabled);
+
 #if defined(USE_X11)
   XInitThreads();
 #endif

content/public/test/unittest_test_suite.h

@@ -8,6 +8,7 @@
 #include <memory>
 
 #include "base/macros.h"
+#include "base/test/scoped_feature_list.h"
 #include "build/build_config.h"
 
 #if defined(USE_AURA)
@@ -39,6 +40,8 @@ class UnitTestTestSuite {
  private:
   std::unique_ptr<base::TestSuite> test_suite_;
 
+  base::test::ScopedFeatureList feature_list_;
+
   std::unique_ptr<TestBlinkWebUnitTestSupport> blink_test_support_;
 #if defined(USE_AURA)
   std::unique_ptr<aura::AuraTestSuiteSetup> aura_test_suite_setup_;

content/shell/browser/shell_browser_main_parts.cc

@@ -139,6 +139,7 @@ int ShellBrowserMainParts::PreEarlyInitialization() {
   net::NetworkChangeNotifier::SetFactory(
       new net::NetworkChangeNotifierFactoryAndroid());
 #endif
+  SetupFieldTrials();
   return RESULT_CODE_NORMAL_EXIT;
 }
 
@@ -180,7 +181,6 @@ void ShellBrowserMainParts::SetupFieldTrials() {
 }
 
 int ShellBrowserMainParts::PreCreateThreads() {
-  SetupFieldTrials();
 #if defined(OS_ANDROID)
   const base::CommandLine* command_line =
       base::CommandLine::ForCurrentProcess();

content/test/test_blink_web_unit_test_support.cc

@@ -5,7 +5,6 @@
 #include "content/test/test_blink_web_unit_test_support.h"
 
 #include "base/callback.h"
-#include "base/feature_list.h"
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/files/scoped_temp_dir.h"
@@ -164,10 +163,6 @@ TestBlinkWebUnitTestSupport::TestBlinkWebUnitTestSupport()
   web_thread_ = renderer_scheduler_->CreateMainThread();
   shared_bitmap_manager_.reset(new cc::TestSharedBitmapManager);
 
-  // Set up a FeatureList instance, so that code using that API will not hit a
-  // an error that it's not set. Cleared by ClearInstanceForTesting() below.
-  base::FeatureList::SetInstance(base::WrapUnique(new base::FeatureList));
-
   // Initialize mojo firstly to enable Blink initialization to use it.
   InitializeMojo();
 
@@ -204,9 +199,6 @@ TestBlinkWebUnitTestSupport::~TestBlinkWebUnitTestSupport() {
   mock_clipboard_.reset();
   if (renderer_scheduler_)
     renderer_scheduler_->Shutdown();
-
-  // Clear the FeatureList that was registered in the constructor.
-  base::FeatureList::ClearInstanceForTesting();
 }
 
 blink::WebBlobRegistry* TestBlinkWebUnitTestSupport::GetBlobRegistry() {