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 e52c35499c165848a4fa11cd452f95dcfebe57a9..580acc90ce2eb83bcbb841969276578e27b15fd5 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"
@@ -1134,6 +1138,11 @@ ServiceRegistry* RenderProcessHostImpl::GetServiceRegistry() {
   return mojo_application_host_->service_registry();
 }
 
+scoped_ptr<base::SharedPersistentMemoryAllocator>
+RenderProcessHostImpl::ExtractMetricsAllocator() {
+  return std::move(metrics_allocator_);
+}
+
 const base::TimeTicks& RenderProcessHostImpl::GetInitTimeForNavigationMetrics()
     const {
   return init_time_;
@@ -2384,6 +2393,30 @@ 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::PersistentHistogramAllocator::GetGlobalAllocator())
+    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(),
+      "RendererMetrics", /*readonly=*/false));
+
+  if (metrics_allocator_) {

[Alexei Svitkine (slow), 2016/03/31 15:22:04]

This if shouldn't be necessary, since a new call above should never return null.

[bcwhite, 2016/03/31 18:27:49]

Done.

+    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.
@@ -2589,6 +2622,9 @@ 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