Reland "[Extensions] Introduce common client initialization"

Relanding since the CL wasn't the cause of test flakiness.

Original change's description:
> [Extensions] Introduce common client initialization
>
> In order to extract apps-specific code from extensions, we'll need to
> be able to add extra information to the extensions client from outside
> extensions code. This will require having a centralized initialization
> for the extensions client.
>
> Introduce a single method, EnsureExtensionsClientInitialized(), which
> constructs and sets the ChromeExtensionsClient. Remove the old way of
> constructing the client, ChromeExtensionsClient::GetInstance(). Update
> all callers to construct the client via the new method.
>
> While we're at it, update the client to use base::NoDestructor instead
> of LazyInstance.
>
> Bug: 873937
> Change-Id: I47147cd5f33ea44079c0a319626c57f3c5813af8
> Reviewed-on: https://chromium-review.googlesource.com/1175459
> Commit-Queue: Devlin <rdevlin.cronin@chromium.org>
> Reviewed-by: Lei Zhang <thestig@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#583217}

TBR=thestig@chromium.org,rdevlin.cronin@chromium.org

Bug: 873937
Change-Id: Idf8fdc2ca89e3f0e481fbfd310c5ebc6067311f1
Reviewed-on: https://chromium-review.googlesource.com/1181162Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Commit-Queue: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584461}

chrome/browser/browser_process_impl.cc

@@ -171,6 +171,7 @@
 #include "chrome/browser/extensions/event_router_forwarder.h"
 #include "chrome/browser/media_galleries/media_file_system_registry.h"
 #include "chrome/browser/ui/apps/chrome_app_window_client.h"
+#include "chrome/common/initialize_extensions_client.h"
 #include "components/storage_monitor/storage_monitor.h"
 #include "extensions/common/extension_l10n_util.h"
 #endif
@@ -259,8 +260,7 @@ void BrowserProcessImpl::Init() {
   extension_event_router_forwarder_ =
       base::MakeRefCounted<extensions::EventRouterForwarder>();
 
-  extensions::ExtensionsClient::Set(
-      extensions::ChromeExtensionsClient::GetInstance());
+  EnsureExtensionsClientInitialized();
 
   extensions_browser_client_ =
       std::make_unique<extensions::ChromeExtensionsBrowserClient>();

chrome/browser/extensions/startup_helper.cc

@@ -14,7 +14,7 @@
 #include "base/strings/utf_string_conversions.h"
 #include "base/task/post_task.h"
 #include "chrome/common/chrome_switches.h"
-#include "chrome/common/extensions/chrome_extensions_client.h"
+#include "chrome/common/initialize_extensions_client.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/common/service_manager_connection.h"
 #include "extensions/browser/extension_file_task_runner.h"
@@ -35,7 +35,7 @@ void PrintPackExtensionMessage(const std::string& message) {
 }  // namespace
 
 StartupHelper::StartupHelper() : pack_job_succeeded_(false) {
-  ExtensionsClient::Set(ChromeExtensionsClient::GetInstance());
+  EnsureExtensionsClientInitialized();
 }
 
 void StartupHelper::OnPackSuccess(

chrome/common/BUILD.gn

@@ -369,6 +369,8 @@ static_library("common") {
       "extensions/sync_helper.h",
       "extensions/webstore_install_result.cc",
       "extensions/webstore_install_result.h",
+      "initialize_extensions_client.cc",
+      "initialize_extensions_client.h",
     ]
     public_deps += [
       "//chrome/common/extensions:mojo_bindings",

chrome/common/extensions/chrome_extensions_client.cc

@@ -96,9 +96,6 @@ ChromeChannelForHistogram GetChromeChannelForHistogram(
 
 }  // namespace
 
-static base::LazyInstance<ChromeExtensionsClient>::Leaky g_client =
-    LAZY_INSTANCE_INITIALIZER;
-
 ChromeExtensionsClient::ChromeExtensionsClient() {}
 
 ChromeExtensionsClient::~ChromeExtensionsClient() {
@@ -345,9 +342,4 @@ std::string ChromeExtensionsClient::GetUserAgent() const {
   return ::GetUserAgent();
 }
 
-// static
-ChromeExtensionsClient* ChromeExtensionsClient::GetInstance() {
-  return g_client.Pointer();
-}
-
 }  // namespace extensions

chrome/common/extensions/chrome_extensions_client.h

@@ -8,7 +8,6 @@
 #include <memory>
 
 #include "base/compiler_specific.h"
-#include "base/lazy_instance.h"
 #include "base/macros.h"
 #include "chrome/common/extensions/permissions/chrome_api_permissions.h"
 #include "chrome/common/extensions/permissions/chrome_permission_message_provider.h"
@@ -57,9 +56,6 @@ class ChromeExtensionsClient : public ExtensionsClient {
   bool ExtensionAPIEnabledInExtensionServiceWorkers() const override;
   std::string GetUserAgent() const override;
 
-  // Get the LazyInstance for ChromeExtensionsClient.
-  static ChromeExtensionsClient* GetInstance();
-
  private:
   const ChromeAPIPermissions chrome_api_permissions_;
   const ExtensionsAPIPermissions extensions_api_permissions_;
@@ -74,8 +70,6 @@ class ChromeExtensionsClient : public ExtensionsClient {
   GURL webstore_base_url_;
   GURL webstore_update_url_;
 
-  friend struct base::LazyInstanceTraitsBase<ChromeExtensionsClient>;
-
   DISALLOW_COPY_AND_ASSIGN(ChromeExtensionsClient);
 };
 

chrome/common/initialize_extensions_client.cc

+// Copyright 2018 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chrome/common/initialize_extensions_client.h"
+
+#include "base/no_destructor.h"
+#include "chrome/common/extensions/chrome_extensions_client.h"
+#include "extensions/common/extensions_client.h"
+
+void EnsureExtensionsClientInitialized() {
+  static bool initialized = false;
+
+  static base::NoDestructor<extensions::ChromeExtensionsClient>
+      extensions_client;
+
+  if (!initialized) {
+    initialized = true;
+    extensions::ExtensionsClient::Set(extensions_client.get());
+  }
+
+  // ExtensionsClient::Set() will early-out if the client was already set, so
+  // this allows us to check that this was the only site setting it.
+  DCHECK_EQ(extensions_client.get(), extensions::ExtensionsClient::Get())
+      << "ExtensionsClient should only be initialized through "
+      << "EnsureExtensionsClientInitialized() when using "
+      << "ChromeExtensionsClient.";
+}

chrome/common/initialize_extensions_client.h

+// Copyright 2018 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_COMMON_INITIALIZE_EXTENSIONS_CLIENT_H_
+#define CHROME_COMMON_INITIALIZE_EXTENSIONS_CLIENT_H_
+
+#include "extensions/buildflags/buildflags.h"
+
+#if !BUILDFLAG(ENABLE_EXTENSIONS)
+#error "Extensions must be enabled"
+#endif
+
+// Initializes the single instance of the ExtensionsClient. Safe to call
+// multiple times.
+void EnsureExtensionsClientInitialized();
+
+#endif  // CHROME_COMMON_INITIALIZE_EXTENSIONS_CLIENT_H_

chrome/renderer/chrome_content_renderer_client.cc

@@ -157,7 +157,7 @@
 #endif
 
 #if BUILDFLAG(ENABLE_EXTENSIONS)
-#include "chrome/common/extensions/chrome_extensions_client.h"
+#include "chrome/common/initialize_extensions_client.h"
 #include "chrome/renderer/extensions/chrome_extensions_renderer_client.h"
 #include "extensions/common/constants.h"
 #include "extensions/common/extension_urls.h"
@@ -353,8 +353,7 @@ ChromeContentRendererClient::ChromeContentRendererClient()
     : main_entry_time_(base::TimeTicks::Now()),
       main_thread_profiler_(ThreadProfiler::CreateAndStartOnMainThread()) {
 #if BUILDFLAG(ENABLE_EXTENSIONS)
-  extensions::ExtensionsClient::Set(
-      extensions::ChromeExtensionsClient::GetInstance());
+  EnsureExtensionsClientInitialized();
   extensions::ExtensionsRendererClient::Set(
       ChromeExtensionsRendererClient::GetInstance());
 #endif

chrome/test/base/chrome_unit_test_suite.cc

@@ -35,8 +35,9 @@
 #endif
 
 #if BUILDFLAG(ENABLE_EXTENSIONS)
-#include "chrome/common/extensions/chrome_extensions_client.h"
+#include "chrome/common/initialize_extensions_client.h"
 #include "extensions/common/extension_paths.h"
+#include "extensions/common/extensions_client.h"
 #endif
 
 namespace {
@@ -50,11 +51,6 @@ class ChromeUnitTestSuiteInitializer : public testing::EmptyTestEventListener {
   void OnTestStart(const testing::TestInfo& test_info) override {
     content_client_.reset(new ChromeContentClient);
     content::SetContentClient(content_client_.get());
-#if BUILDFLAG(ENABLE_EXTENSIONS)
-    extensions::ExtensionsClient::Get()->InitializeWebStoreUrls(
-        base::CommandLine::ForCurrentProcess());
-
-#endif
 
     browser_content_client_.reset(new ChromeContentBrowserClient());
     content::SetBrowserClientForTesting(browser_content_client_.get());
@@ -135,8 +131,7 @@ void ChromeUnitTestSuite::InitializeProviders() {
 #if BUILDFLAG(ENABLE_EXTENSIONS)
   extensions::RegisterPathProvider();
 
-  extensions::ExtensionsClient::Set(
-      extensions::ChromeExtensionsClient::GetInstance());
+  EnsureExtensionsClientInitialized();
 #endif
 
   content::WebUIControllerFactory::RegisterFactory(