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

content/public/test/mock_render_process_host.cc

Index: content/public/test/mock_render_process_host.cc
diff --git a/content/public/test/mock_render_process_host.cc b/content/public/test/mock_render_process_host.cc
index 0fa30ed7d731e775b473657cc22b2e9bafa806d3..d917115615078be764a5d7060999627f24361c0d 100644
--- a/content/public/test/mock_render_process_host.cc
+++ b/content/public/test/mock_render_process_host.cc
@@ -263,6 +263,11 @@ ServiceRegistry* MockRenderProcessHost::GetServiceRegistry() {
   return service_registry_.get();
 }
 
+scoped_ptr<base::SharedPersistentMemoryAllocator>
+MockRenderProcessHost::ExtractMetricsAllocator() {
+  return std::move(metrics_allocator_);
+}
+
 const base::TimeTicks& MockRenderProcessHost::GetInitTimeForNavigationMetrics()
     const {
   static base::TimeTicks dummy_time = base::TimeTicks::Now();