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

content/public/browser/render_process_host.h

Index: content/public/browser/render_process_host.h
diff --git a/content/public/browser/render_process_host.h b/content/public/browser/render_process_host.h
index 62d65fca999490f31592be64bad59f5327b45c8c..dfe7690f35881100cda207c7c81d3467254b7044 100644
--- a/content/public/browser/render_process_host.h
+++ b/content/public/browser/render_process_host.h
@@ -22,6 +22,7 @@
 class GURL;
 
 namespace base {
+class SharedPersistentMemoryAllocator;
 class TimeDelta;
 }
 
@@ -258,6 +259,10 @@ class CONTENT_EXPORT RenderProcessHost : public IPC::Sender,
   // Returns the ServiceRegistry for this process.
   virtual ServiceRegistry* GetServiceRegistry() = 0;
 
+  // Returns any persistent-memory-allocator used for renderer metrics.
+  virtual scoped_ptr<base::SharedPersistentMemoryAllocator>
+  GetMetricsAllocator() = 0;
+
   // PlzNavigate
   // Returns the time the first call to Init completed successfully (after a new
   // renderer process was created); further calls to Init won't change this