Use persistent memory for receiving metrics from sub-processes.

content/public/browser/browser_child_process_host.h

Index: content/public/browser/browser_child_process_host.h
diff --git a/content/public/browser/browser_child_process_host.h b/content/public/browser/browser_child_process_host.h
index 60334a9afa2c4499f1e5c3342c875c032d42dc6a..3ae4d3f1eabb623d5506737e3c08887d975e3455 100644
--- a/content/public/browser/browser_child_process_host.h
+++ b/content/public/browser/browser_child_process_host.h
@@ -21,6 +21,7 @@
 namespace base {
 class CommandLine;
 class FilePath;
+class SharedPersistentMemoryAllocator;
 }
 
 namespace shell {
@@ -82,6 +83,10 @@ class CONTENT_EXPORT BrowserChildProcessHost : public IPC::Sender {
   virtual base::TerminationStatus GetTerminationStatus(
       bool known_dead, int* exit_code) = 0;
 
+  // Take ownership of a "shared" metrics allocator (if one exists).
+  virtual std::unique_ptr<base::SharedPersistentMemoryAllocator>
+  TakeMetricsAllocator() = 0;
+
   // Sets the user-visible name of the process.
   virtual void SetName(const base::string16& name) = 0;