Move MemoryPressureObserverChromeOS instantiation from Chrome to Content

There are several proposed content CLs which are making use of the MemoryPressureObserverChromeOS::GetCurrentPressureLevel() call to adapt dynamically to the current memory pressure. Examples: The |OomPriorityManager|, the |RendererFrameManager|, ...

BUG=440556
TEST=-

Review URL: https://codereview.chromium.org/800603002

Cr-Commit-Position: refs/heads/master@{#308459}

chrome/browser/chromeos/chrome_browser_main_chromeos.cc

@@ -11,7 +11,6 @@
 #include "ash/shell.h"
 #include "base/bind.h"
 #include "base/callback.h"
-#include "base/chromeos/memory_pressure_observer_chromeos.h"
 #include "base/command_line.h"
 #include "base/files/file_util.h"
 #include "base/lazy_instance.h"
@@ -333,12 +332,6 @@ void ChromeBrowserMainPartsChromeos::PreMainMessageLoopStart() {
 }
 
 void ChromeBrowserMainPartsChromeos::PostMainMessageLoopStart() {
-  // Instantiate the MemoryPressureObserver.
-  if (CommandLine::ForCurrentProcess()->HasSwitch(
-          switches::kUseMemoryPressureSystemChromeOS)) {
-    memory_pressure_observer_.reset(new base::MemoryPressureObserverChromeOS);
-  }
-
   base::FilePath user_data_dir;
   if (!base::SysInfo::IsRunningOnChromeOS() &&
       PathService::Get(chrome::DIR_USER_DATA, &user_data_dir)) {
@@ -708,9 +701,6 @@ void ChromeBrowserMainPartsChromeos::PostBrowserStart() {
 void ChromeBrowserMainPartsChromeos::PostMainMessageLoopRun() {
   BootTimesLoader::Get()->AddLogoutTimeMarker("UIMessageLoopEnded", true);
 
-  // Remove the MemoryPressureObserver since it is not needed anymore.
-  memory_pressure_observer_.reset();
-
   g_browser_process->platform_part()->oom_priority_manager()->Stop();
 
   // Early wake-up of HID device service.

chrome/browser/chromeos/chrome_browser_main_chromeos.h

@@ -11,10 +11,6 @@
 #include "chrome/browser/chromeos/external_metrics.h"
 #include "chromeos/system/version_loader.h"
 
-namespace base {
-class MemoryPressureObserverChromeOS;
-}
-
 namespace content {
 class PowerSaveBlocker;
 }
@@ -90,8 +86,6 @@ class ChromeBrowserMainPartsChromeos : public ChromeBrowserMainPartsLinux {
 
   scoped_refptr<chromeos::ExternalMetrics> external_metrics_;
 
-  scoped_ptr<base::MemoryPressureObserverChromeOS> memory_pressure_observer_;
-
   bool use_new_network_change_notifier_;
 
   DISALLOW_COPY_AND_ASSIGN(ChromeBrowserMainPartsChromeos);

content/browser/browser_main_loop.cc

@@ -100,6 +100,11 @@
 #include "ui/base/l10n/l10n_util_win.h"
 #endif
 
+#if defined(OS_CHROMEOS)
+#include "base/chromeos/memory_pressure_observer_chromeos.h"
+#include "chromeos/chromeos_switches.h"
+#endif
+
 #if defined(USE_GLIB)
 #include <glib-object.h>
 #endif
@@ -475,7 +480,12 @@ void BrowserMainLoop::MainMessageLoopStart() {
     l10n_util::OverrideLocaleWithUILanguageList();
   }
 #endif
-
+#if defined(OS_CHROMEOS)
+  if (CommandLine::ForCurrentProcess()->HasSwitch(
+          chromeos::switches::kUseMemoryPressureSystemChromeOS)) {
+    memory_pressure_observer_.reset(new base::MemoryPressureObserverChromeOS);
+  }
+#endif
   // Create a MessageLoop if one does not already exist for the current thread.
   if (!base::MessageLoop::current())
     main_message_loop_.reset(new base::MessageLoopForUI);
@@ -823,6 +833,10 @@ void BrowserMainLoop::ShutdownThreadsAndCleanUp() {
     resource_dispatcher_host_.get()->Shutdown();
   }
 
+#if defined(OS_CHROMEOS)
+  memory_pressure_observer_.reset();
+#endif
+
 #if defined(OS_MACOSX)
   BrowserCompositorMac::DisableRecyclingForShutdown();
 #endif

content/browser/browser_main_loop.h

@@ -20,6 +20,9 @@ class HighResolutionTimerManager;
 class MessageLoop;
 class PowerMonitor;
 class SystemMonitor;
+#if defined(OS_CHROMEOS)
+class MemoryPressureObserverChromeOS;
+#endif
 namespace debug {
 class TraceMemoryController;
 class TraceEventSystemStatsMonitor;
@@ -115,6 +118,12 @@ class CONTENT_EXPORT BrowserMainLoop {
     return device_monitor_mac_.get();
   }
 #endif
+#if defined(OS_CHROMEOS)
+  // Return the MemoryPressureObserver which might be NULL.
+  base::MemoryPressureObserverChromeOS* memory_pressure_observer() {
+    return memory_pressure_observer_.get();
+  }
+#endif
 
  private:
   class MemoryObserver;
@@ -171,6 +180,9 @@ class CONTENT_EXPORT BrowserMainLoop {
 #if defined(OS_ANDROID)
   // Android implementation of ScreenOrientationDelegate
   scoped_ptr<ScreenOrientationDelegate> screen_orientation_delegate_;
+#endif
+#if defined(OS_CHROMEOS)
+  scoped_ptr<base::MemoryPressureObserverChromeOS> memory_pressure_observer_;
 #endif
   // The startup task runner is created by CreateStartupTasks()
   scoped_ptr<StartupTaskRunner> startup_task_runner_;