[Tentaive patch for discussion] Add Purge+Suspend metrics as UMA.

content/renderer/render_thread_impl.h

Index: content/renderer/render_thread_impl.h
diff --git a/content/renderer/render_thread_impl.h b/content/renderer/render_thread_impl.h
index f769d4febaeefd756ec5d287276ae0dec35a61b0..2a44c7e57ee8edd7a1c59c1e63b4312c573efcfe 100644
--- a/content/renderer/render_thread_impl.h
+++ b/content/renderer/render_thread_impl.h
@@ -22,6 +22,7 @@
 #include "base/threading/thread_checker.h"
 #include "base/timer/timer.h"
 #include "build/build_config.h"
+#include "content/child/child_discardable_shared_memory_manager.h"
 #include "content/child/child_thread_impl.h"
 #include "content/child/memory/child_memory_coordinator_impl.h"
 #include "content/common/content_export.h"
@@ -39,6 +40,7 @@
 #include "net/base/network_change_notifier.h"
 #include "third_party/WebKit/public/platform/WebConnectionType.h"
 #include "third_party/WebKit/public/platform/scheduler/renderer/renderer_scheduler.h"
+#include "third_party/WebKit/public/web/WebMemoryStatistics.h"
 #include "ui/gfx/native_widget_types.h"
 
 #if defined(OS_MACOSX)
@@ -475,6 +477,7 @@ class CONTENT_EXPORT RenderThreadImpl
   bool OnControlMessageReceived(const IPC::Message& msg) override;
   void OnProcessBackgrounded(bool backgrounded) override;
   void OnProcessPurgeAndSuspend() override;
+
   void RecordAction(const base::UserMetricsAction& action) override;
   void RecordComputedAction(const std::string& action) override;
 
@@ -527,6 +530,8 @@ class CONTENT_EXPORT RenderThreadImpl
   void OnRendererHidden();
   void OnRendererVisible();
 
+  void OnDumpMemoryUsage() const;
+
   void ReleaseFreeMemory();
 
   void OnSyncMemoryPressure(