Use persistent memory for receiving metrics from sub-processes.

content/browser/browser_child_process_host_impl.h

Index: content/browser/browser_child_process_host_impl.h
diff --git a/content/browser/browser_child_process_host_impl.h b/content/browser/browser_child_process_host_impl.h
index 082fdf6e193507030dabc263b2aa3b37de2b7f59..f83be3c730c67e7ecd1587365eecc674ded3ea5c 100644
--- a/content/browser/browser_child_process_host_impl.h
+++ b/content/browser/browser_child_process_host_impl.h
@@ -15,6 +15,7 @@
 #include "base/memory/weak_ptr.h"
 #include "base/process/process.h"
 #include "base/single_thread_task_runner.h"
+#include "base/strings/string_piece.h"
 #include "base/synchronization/waitable_event_watcher.h"
 #include "build/build_config.h"
 #include "content/browser/child_process_launcher.h"
@@ -54,7 +55,9 @@ class CONTENT_EXPORT BrowserChildProcessHostImpl
  public:
   BrowserChildProcessHostImpl(content::ProcessType process_type,
                               BrowserChildProcessHostDelegate* delegate,
-                              const std::string& mojo_child_token);
+                              const std::string& mojo_child_token,
+                              size_t shared_metrics_memory_size,
+                              base::StringPiece shared_metrics_name);
   ~BrowserChildProcessHostImpl() override;
 
   // Terminates all child processes and deletes each BrowserChildProcessHost
@@ -75,6 +78,8 @@ class CONTENT_EXPORT BrowserChildProcessHostImpl
   ChildProcessHost* GetHost() const override;
   base::TerminationStatus GetTerminationStatus(bool known_dead,
                                                int* exit_code) override;
+  std::unique_ptr<base::SharedPersistentMemoryAllocator> TakeMetricsAllocator()
+      override;
   void SetName(const base::string16& name) override;
   void SetHandle(base::ProcessHandle handle) override;
   shell::InterfaceProvider* GetRemoteInterfaces() override;
@@ -115,6 +120,11 @@ class CONTENT_EXPORT BrowserChildProcessHostImpl
   static void AddObserver(BrowserChildProcessObserver* observer);
   static void RemoveObserver(BrowserChildProcessObserver* observer);
 
+  // Passes the |metrics_allocator_|, if any, to the managed process. This
+  // requires the process to have been launched and the RPC channel to be
+  // available.
+  void ShareMetricsAllocatorToProcess();
+
   // ChildProcessLauncher::Client implementation.
   void OnProcessLaunched() override;
   void OnProcessLaunchFailed(int error_code) override;
@@ -149,6 +159,9 @@ class CONTENT_EXPORT BrowserChildProcessHostImpl
   base::win::ObjectWatcher early_exit_watcher_;
 #endif
 
+  // The memory allocator, if any, in which the process will write its metrics.
+  std::unique_ptr<base::SharedPersistentMemoryAllocator> metrics_allocator_;
+
   bool is_channel_connected_;
   bool notify_child_disconnected_;