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

content/browser/renderer_host/render_process_host_impl.cc

Index: content/browser/renderer_host/render_process_host_impl.cc
diff --git a/content/browser/renderer_host/render_process_host_impl.cc b/content/browser/renderer_host/render_process_host_impl.cc
index 5ba612b18bf6b304bfbd7ac8088b7694a5514d5e..7facd9f1c637fea4d50d0c67039a3ad387c71b69 100644
--- a/content/browser/renderer_host/render_process_host_impl.cc
+++ b/content/browser/renderer_host/render_process_host_impl.cc
@@ -24,8 +24,12 @@
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/macros.h"
+#include "base/memory/shared_memory.h"
+#include "base/memory/shared_memory_handle.h"
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram.h"
+#include "base/metrics/persistent_histogram_allocator.h"
+#include "base/metrics/persistent_memory_allocator.h"
 #include "base/process/process_handle.h"
 #include "base/rand_util.h"
 #include "base/single_thread_task_runner.h"
@@ -1121,6 +1125,11 @@ ServiceRegistry* RenderProcessHostImpl::GetServiceRegistry() {
   return mojo_application_host_->service_registry();
 }
 
+scoped_ptr<base::SharedPersistentMemoryAllocator>
+RenderProcessHostImpl::TakeMetricsAllocator() {
+  return std::move(metrics_allocator_);
+}
+
 const base::TimeTicks& RenderProcessHostImpl::GetInitTimeForNavigationMetrics()
     const {
   return init_time_;
@@ -2360,6 +2369,28 @@ void RenderProcessHostImpl::RegisterProcessHostForSite(
     map->RegisterProcess(site, process);
 }
 
+void RenderProcessHostImpl::CreateSharedRendererHistogramAllocator() {
+  DCHECK(!metrics_allocator_);
+
+  // Create a persistent memory segment for renderer histograms only if
+  // they're active in the browser.
+  if (!base::GlobalHistogramAllocator::Get())
+    return;
+
+  // TODO(bcwhite): Update this with the correct memory size.
+  scoped_ptr<base::SharedMemory> shm(new base::SharedMemory());
+  shm->CreateAndMapAnonymous(2 << 20);  // 2 MiB
+  metrics_allocator_.reset(new base::SharedPersistentMemoryAllocator(
+      std::move(shm), child_process_launcher_->GetProcess().Pid(),

[Will Harris, 2016/04/07 00:29:41]

use RenderProcessHostImpl::GetHandle here

also, do you plan to handle run_renderer_in_process() being true, if so you
might not have a child_process_launcher_

[bcwhite, 2016/04/07 01:15:55]

It looks like GetId() is a better choice; I just need some sort of identifying
number.
Check added.

+      "RendererMetrics", /*readonly=*/false));
+
+  base::SharedMemoryHandle shm_handle;
+  metrics_allocator_->shared_memory()->ShareToProcess(
+      child_process_launcher_->GetProcess().Handle(), &shm_handle);
+  Send(new ChildProcessMsg_SetHistogramMemory(
+      shm_handle, metrics_allocator_->shared_memory()->mapped_size()));
+}
+
 void RenderProcessHostImpl::ProcessDied(bool already_dead,
                                         RendererClosedDetails* known_details) {
   // Our child process has died.  If we didn't expect it, it's a crash.
@@ -2565,6 +2596,9 @@ void RenderProcessHostImpl::OnProcessLaunched() {
 #else
     UpdateProcessPriority();
 #endif
+
+    // Share histograms between the renderer and this process.
+    CreateSharedRendererHistogramAllocator();
   }
 
   // NOTE: This needs to be before sending queued messages because