Enable spare RenderProcessHost to be preinitialized.

content/public/browser/render_process_host.h

Index: content/public/browser/render_process_host.h
diff --git a/content/public/browser/render_process_host.h b/content/public/browser/render_process_host.h
index 778f93da8ceffbb9c6fa48d053c098f332289d64..e6444cfb7ed404b651e8b0bbc2733da63f9abe48 100644
--- a/content/public/browser/render_process_host.h
+++ b/content/public/browser/render_process_host.h
@@ -377,6 +377,12 @@ class CONTENT_EXPORT RenderProcessHost : public IPC::Sender,
 
   // Static management functions -----------------------------------------------
 
+  // Possibly start an unbound, spare RenderProcessHost. A subsequent call to
+  // CreateRenderProcessHost with a matching browser_context may use this
+  // preinitialized RenderProcessHost, improving performance.
+  static void StartSpareRenderProcessHost(
+      content::BrowserContext* browser_context);
+
   // Flag to run the renderer in process.  This is primarily
   // for debugging purposes.  When running "in process", the
   // browser maintains a single RenderProcessHost which communicates