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

content/browser/renderer_host/render_process_host_impl.cc

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Represents the browser side of the browser <--> renderer communication
 // channel. There will be one RenderProcessHost per renderer process.
 
 #include "content/browser/renderer_host/render_process_host_impl.h"
 
 #include <algorithm>
 #include <limits>
 #include <utility>
 #include <vector>
 
 #include "base/base_switches.h"
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/callback.h"
 #include "base/command_line.h"
 #include "base/debug/dump_without_crashing.h"
 #include "base/feature_list.h"
 #include "base/files/file.h"
 #include "base/lazy_instance.h"
 #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"
 #include "base/stl_util.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/supports_user_data.h"
 #include "base/sys_info.h"
 #include "base/threading/thread.h"
 #include "base/threading/thread_restrictions.h"
 #include "base/trace_event/trace_event.h"
@@ skipping 1088 matching lines @@
 
 void RenderProcessHostImpl::NotifyTimezoneChange(const std::string& zone_id) {
   Send(new ViewMsg_TimezoneChange(zone_id));
 }
 
 ServiceRegistry* RenderProcessHostImpl::GetServiceRegistry() {
   DCHECK(mojo_application_host_);
   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_;
 }
 
 bool RenderProcessHostImpl::SubscribeUniformEnabled() const {
   return subscribe_uniform_enabled_;
 }
 
 void RenderProcessHostImpl::OnAddSubscription(unsigned int target) {
@@ skipping 1435 matching lines @@
     // Experiment with not setting the initial priority of a renderer, as this
     // might be a visible tab but since no widgets are currently present, it
     // will get backgrounded. See https://crbug.com/560446.
     if (base::FeatureList::IsEnabled(
             features::kUpdateRendererPriorityOnStartup)) {
       UpdateProcessPriority();
     }
 #else
     UpdateProcessPriority();
 #endif
+
+    // Create a persistent memory segment for renderer histograms only if

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

Please make a separate function for this block to encapsulate the logic.

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

Done.

+    // they're active in the browser.
+    if (base::PersistentHistogramAllocator::GetGlobalAllocator()) {
+      DCHECK(!metrics_allocator_);
+      // 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_) {
+        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()));
+      }
+    }
   }
 
   // NOTE: This needs to be before sending queued messages because
   // ExtensionService uses this notification to initialize the renderer process
   // with state that must be there before any JavaScript executes.
   //
   // The queued messages contain such things as "navigate". If this notification
   // was after, we can end up executing JavaScript before the initialization
   // happens.
   NotificationService::current()->Notify(NOTIFICATION_RENDERER_PROCESS_CREATED,
@@ skipping 213 matching lines @@
 
     // Skip widgets in other processes.
     if (rvh->GetProcess()->GetID() != GetID())
       continue;
 
     rvh->OnWebkitPreferencesChanged();
   }
 }
 
 }  // namespace content