Per-host V8 histograms.

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 d39fb9e9e0c38360c1ae8a01df9460a88cd8bc3f..f991b19d5748619279b59cc85770ee347a5a995d 100644
--- a/content/renderer/render_thread_impl.h
+++ b/content/renderer/render_thread_impl.h
@@ -238,6 +238,17 @@ class CONTENT_EXPORT RenderThreadImpl : public content::RenderThread,
   // first call.
   content::AudioRendererMixerManager* GetAudioRendererMixerManager();
 
+  // Called when a top frame of a RenderView navigates. This function updates
+  // RenderViewThread's information about whether all RenderViews are displaying

[Charlie Reis, 2012/08/22 23:09:59]

nit: RenderViewThread -> RenderThreadImpl?

[marja, 2012/08/23 14:15:00]

Done.

+  // a page from the same host. |host| is the host where a RenderView navigated,
+  // and |view_count| is the number of RenderViews in this process.
+  void RenderViewNavigatedToHost(const std::string& host, size_t view_count);
+
+  // Used for customizing some histograms if all RenderViews share the same
+  // host. Returns the current custom histogram name to use for
+  // |histogram_name|, or |histogram_name| if it shouldn't be customized.
+  std::string ConvertToCustomHistogramName(const char* histogram_name);
+
  private:
   virtual bool OnControlMessageReceived(const IPC::Message& msg) OVERRIDE;
 
@@ -254,6 +265,15 @@ class CONTENT_EXPORT RenderThreadImpl : public content::RenderThread,
 
   void IdleHandlerInForegroundTab();
 
+  // Used for updating the information on which is the common host which all
+  // RenderView's share (if any). If there is no common host, this function is
+  // called with an empty string.
+  void SetCommonHost(const std::string& host);
+
+  // For initializing information about which histograms should be customized
+  // per host.
+  void InitializeCustomHistograms();
+
   // These objects live solely on the render thread.
   scoped_ptr<AppCacheDispatcher> appcache_dispatcher_;
   scoped_ptr<DomStorageDispatcher> dom_storage_dispatcher_;
@@ -318,6 +338,11 @@ class CONTENT_EXPORT RenderThreadImpl : public content::RenderThread,
 
   scoped_ptr<content::AudioRendererMixerManager> audio_renderer_mixer_manager_;
 
+  // For producing custom histograms if all RenderViews share the same host.

[Charlie Reis, 2012/08/22 23:09:59]

Can you say a bit more?  e.g., that the histogram names in the set will be
customized with a site-specific suffix if the process is only used for pages
from a set of known sites?

[marja, 2012/08/23 14:15:00]

Done.

+  std::string common_host_;
+  std::string custom_page_;

[Charlie Reis, 2012/08/22 23:09:59]

custom_page_ doesn't reveal much about what it's for.  Maybe
common_host_histogram_suffix_?

[marja, 2012/08/23 14:15:00]

Done.

+  std::set<std::string> custom_histograms_;
+
   DISALLOW_COPY_AND_ASSIGN(RenderThreadImpl);
 };