Move enable extensions define to a build flag.

chrome/browser/browser_process_impl.cc

Index: chrome/browser/browser_process_impl.cc
diff --git a/chrome/browser/browser_process_impl.cc b/chrome/browser/browser_process_impl.cc
index 3066504299868e9104db0311eef627697415c292..b07dbac05243d4a0f093fac4fca71812c0682dc8 100644
--- a/chrome/browser/browser_process_impl.cc
+++ b/chrome/browser/browser_process_impl.cc
@@ -117,6 +117,7 @@
 #include "content/public/browser/storage_partition.h"
 #include "content/public/common/content_switches.h"
 #include "extensions/common/constants.h"
+#include "extensions/features/features.h"
 #include "net/socket/client_socket_pool_manager.h"
 #include "net/url_request/url_request_context_getter.h"
 #include "printing/features/features.h"
@@ -143,7 +144,7 @@
 #include "chrome/browser/background/background_mode_manager.h"
 #endif
 
-#if defined(ENABLE_EXTENSIONS)
+#if BUILDFLAG(ENABLE_EXTENSIONS)
 #include "chrome/browser/extensions/chrome_extensions_browser_client.h"
 #include "chrome/browser/extensions/event_router_forwarder.h"
 #include "chrome/browser/media_galleries/media_file_system_registry.h"
@@ -236,7 +237,7 @@ BrowserProcessImpl::BrowserProcessImpl(
 
   device_client_.reset(new ChromeDeviceClient);
 
-#if defined(ENABLE_EXTENSIONS)
+#if BUILDFLAG(ENABLE_EXTENSIONS)
   // Athena sets its own instance during Athena's init process.
   extensions::AppWindowClient::Set(ChromeAppWindowClient::GetInstance());
 
@@ -261,7 +262,7 @@ BrowserProcessImpl::BrowserProcessImpl(
 }
 
 BrowserProcessImpl::~BrowserProcessImpl() {
-#if defined(ENABLE_EXTENSIONS)
+#if BUILDFLAG(ENABLE_EXTENSIONS)
   extensions::ExtensionsBrowserClient::Set(nullptr);
 #endif
 
@@ -323,7 +324,7 @@ void BrowserProcessImpl::StartTearDown() {
 
   child_process_watcher_.reset();
 
-#if defined(ENABLE_EXTENSIONS)
+#if BUILDFLAG(ENABLE_EXTENSIONS)
   media_file_system_registry_.reset();
   // Remove the global instance of the Storage Monitor now. Otherwise the
   // FILE thread would be gone when we try to release it in the dtor and
@@ -571,7 +572,7 @@ BrowserProcessPlatformPart* BrowserProcessImpl::platform_part() {
 
 extensions::EventRouterForwarder*
 BrowserProcessImpl::extension_event_router_forwarder() {
-#if defined(ENABLE_EXTENSIONS)
+#if BUILDFLAG(ENABLE_EXTENSIONS)
   return extension_event_router_forwarder_.get();
 #else
   return NULL;
@@ -716,7 +717,7 @@ const std::string& BrowserProcessImpl::GetApplicationLocale() {
 
 void BrowserProcessImpl::SetApplicationLocale(const std::string& locale) {
   locale_ = locale;
-#if defined(ENABLE_EXTENSIONS)
+#if BUILDFLAG(ENABLE_EXTENSIONS)
   extension_l10n_util::SetProcessLocale(locale);
 #endif
   ChromeContentBrowserClient::SetApplicationLocale(locale);
@@ -729,7 +730,7 @@ DownloadStatusUpdater* BrowserProcessImpl::download_status_updater() {
 }
 
 MediaFileSystemRegistry* BrowserProcessImpl::media_file_system_registry() {
-#if defined(ENABLE_EXTENSIONS)
+#if BUILDFLAG(ENABLE_EXTENSIONS)
   if (!media_file_system_registry_)
     media_file_system_registry_.reset(new MediaFileSystemRegistry());
   return media_file_system_registry_.get();
@@ -1035,7 +1036,7 @@ void BrowserProcessImpl::CreateLocalState() {
 }
 
 void BrowserProcessImpl::PreCreateThreads() {
-#if defined(ENABLE_EXTENSIONS)
+#if BUILDFLAG(ENABLE_EXTENSIONS)
   // Register the chrome-extension scheme to reflect the extension process
   // model. Controlled by a field trial, so we can't do this earlier.
   base::FieldTrialList::FindFullName("SiteIsolationExtensions");