Create and pass shared-histogram-allocator from browser to renderer.

content/browser/renderer_host/render_process_host_impl.h

Index: content/browser/renderer_host/render_process_host_impl.h
diff --git a/content/browser/renderer_host/render_process_host_impl.h b/content/browser/renderer_host/render_process_host_impl.h
index ccb83b2a16c3919a1797502f44987c1c39051172..299aa70e0aaa6624aa0059e7fdb94f19611648dd 100644
--- a/content/browser/renderer_host/render_process_host_impl.h
+++ b/content/browser/renderer_host/render_process_host_impl.h
@@ -155,6 +155,8 @@ class CONTENT_EXPORT RenderProcessHostImpl
   void ResumeDeferredNavigation(const GlobalRequestID& request_id) override;
   void NotifyTimezoneChange(const std::string& timezone) override;
   ServiceRegistry* GetServiceRegistry() override;
+  scoped_ptr<base::SharedPersistentMemoryAllocator> ExtractMetricsAllocator()

[grt (UTC plus 2), 2016/04/01 14:22:49]

nit: TakeMetricsAllocator() for consistency with other functions that pass
ownership of a thing to the caller.

[bcwhite, 2016/04/01 16:50:26]

Done.

+      override;
   const base::TimeTicks& GetInitTimeForNavigationMetrics() const override;
   bool SubscribeUniformEnabled() const override;
   void OnAddSubscription(unsigned int target) override;
@@ -328,6 +330,12 @@ class CONTENT_EXPORT RenderProcessHostImpl
   // change.
   void UpdateProcessPriority();
 
+  // Creates a PersistentMemoryAllocator and shares it with the renderer
+  // process for it to store histograms from that process. The allocator is
+  // available for extraction by a SubprocesMetricsProvider in order to
+  // report those histograms to UMA.
+  void CreateSharedRendererHistogramAllocator();
+
   // Handle termination of our process.
   void ProcessDied(bool already_dead, RendererClosedDetails* known_details);
 
@@ -505,6 +513,9 @@ class CONTENT_EXPORT RenderProcessHostImpl
   // Whether or not the CHROMIUM_subscribe_uniform WebGL extension is enabled
   bool subscribe_uniform_enabled_;
 
+  // The memory allocator, if any, in which the renderer will write its metrics.
+  scoped_ptr<base::SharedPersistentMemoryAllocator> metrics_allocator_;
+
   bool channel_connected_;
   bool sent_render_process_ready_;