Enable spare RenderProcessHost to be preinitialized.

content/browser/renderer_host/render_process_host_impl.h

Index: content/browser/renderer_host/render_process_host_impl.h
diff --git a/content/browser/renderer_host/render_process_host_impl.h b/content/browser/renderer_host/render_process_host_impl.h
index 96900941e917bf964a13293930b129bb36f9ab78..3661bd5ccb91784cbee7718d9d8e6ed60c6c268f 100644
--- a/content/browser/renderer_host/render_process_host_impl.h
+++ b/content/browser/renderer_host/render_process_host_impl.h
@@ -114,9 +114,11 @@ class CONTENT_EXPORT RenderProcessHostImpl
       public NON_EXPORTED_BASE(mojom::AssociatedInterfaceProvider),
       public NON_EXPORTED_BASE(mojom::RendererHost) {
  public:
-  RenderProcessHostImpl(BrowserContext* browser_context,
-                        StoragePartitionImpl* storage_partition_impl,
-                        bool is_for_guests_only);
+  static RenderProcessHost* CreateRenderProcessHost(

[Charlie Reis, 2017/06/28 22:31:35]

Let's include a comment here suggesting that callers consider using the spare
RPH if it's available and matches (e.g., using the helper method I'm
requesting).

[mattcary, 2017/06/29 12:57:09]

Done, along with the addition of the alternative constructor you suggest.

+      BrowserContext* browser_context,
+      StoragePartitionImpl* storage_partition_impl,
+      bool is_for_guests_only);
+
   ~RenderProcessHostImpl() override;
 
   // RenderProcessHost implementation (public portion).
@@ -335,6 +337,14 @@ class CONTENT_EXPORT RenderProcessHostImpl
       RenderProcessHost* render_process_host,
       const GURL& site_url);
 
+  // This should be called when a storage partition is shutdown and will cleanup
+  // any RenderProcessHosts associated with the partition.
+  static void OnStoragePartitionShutdown(StoragePartition* partition);
+
+  // Return the spare RenderProcessHost, if it exists. There is at most one
+  // globally-used spare RenderProcessHost at any time.
+  static RenderProcessHost* GetSpareRenderProcessHostForTesting();
+
  protected:
   // A proxy for our IPC::Channel that lives on the IO thread.
   std::unique_ptr<IPC::ChannelProxy> channel_;
@@ -361,6 +371,12 @@ class CONTENT_EXPORT RenderProcessHostImpl
   class ConnectionFilterController;
   class ConnectionFilterImpl;
 
+  // Use CreateRenderProcessHost() instead of calling this constructor
+  // directly.
+  RenderProcessHostImpl(BrowserContext* browser_context,
+                        StoragePartitionImpl* storage_partition_impl,
+                        bool is_for_guests_only);
+
   // Initializes a new IPC::ChannelProxy in |channel_|, which will be connected
   // to the next child process launched for this host, if any.
   void InitializeChannelProxy();