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

content/public/test/mock_render_process_host.h

Index: content/public/test/mock_render_process_host.h
diff --git a/content/public/test/mock_render_process_host.h b/content/public/test/mock_render_process_host.h
index d6dcea0e02899415f87600806604c33400fc1de4..2da4f6e5d7089556204f8ac6c8446e3975d620eb 100644
--- a/content/public/test/mock_render_process_host.h
+++ b/content/public/test/mock_render_process_host.h
@@ -11,6 +11,7 @@
 
 #include "base/macros.h"
 #include "base/memory/scoped_vector.h"
+#include "base/metrics/persistent_memory_allocator.h"
 #include "base/observer_list.h"
 #include "content/public/browser/render_process_host.h"
 #include "content/public/browser/render_process_host_factory.h"
@@ -92,6 +93,8 @@ class MockRenderProcessHost : public RenderProcessHost {
   void ResumeDeferredNavigation(const GlobalRequestID& request_id) override;
   void NotifyTimezoneChange(const std::string& zone_id) override;
   ServiceRegistry* GetServiceRegistry() override;
+  scoped_ptr<base::SharedPersistentMemoryAllocator> GetMetricsAllocator()
+      override;

[Alexei Svitkine (slow), 2016/03/24 17:29:53]

I think it's pretty strange for the function to be called Get*() but for it to
transfer ownership. Please use a different name that makes it clear that
ownership is being transferred and document the use case in the comment for this
function in the interface.

[bcwhite, 2016/03/29 11:53:27]

Done.

   const base::TimeTicks& GetInitTimeForNavigationMetrics() const override;
   bool SubscribeUniformEnabled() const override;
   void OnAddSubscription(unsigned int target) override;
@@ -140,6 +143,11 @@ class MockRenderProcessHost : public RenderProcessHost {
     service_registry_ = std::move(service_registry);
   }
 
+  void SetMetricsAllocator(

[Alexei Svitkine (slow), 2016/03/24 17:29:53]

What calls this?

[bcwhite, 2016/03/29 11:53:27]

Nothing.  But since it's a mock and allows extraction of the allocator, it
seemed a good idea to add a method to inject it.

[Alexei Svitkine (slow), 2016/03/29 17:51:24]

I don't think we should add it if it's not needed. If it becomes needed, it can
be added by the CL that needs it. Also, you can remove the member variable as
well and make the getter return null.

[bcwhite, 2016/03/30 21:25:55]

Done.

+      scoped_ptr<base::SharedPersistentMemoryAllocator> allocator) {
+    metrics_allocator_ = std::move(allocator);
+  }
+
  private:
   // Stores IPC messages that would have been sent to the renderer.
   IPC::TestSink sink_;
@@ -160,6 +168,7 @@ class MockRenderProcessHost : public RenderProcessHost {
   scoped_ptr<base::ProcessHandle> process_handle;
   int worker_ref_count_;
   scoped_ptr<ServiceRegistry> service_registry_;
+  scoped_ptr<base::SharedPersistentMemoryAllocator> metrics_allocator_;
 
   DISALLOW_COPY_AND_ASSIGN(MockRenderProcessHost);
 };