Switch RenderFrameHostManager to use RenderProcessHostObserver, remove NOTIFICATION_RENDERER_PROCES…

content/public/browser/render_process_host_observer.h

 // Copyright 2013 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.
 
 #ifndef CONTENT_PUBLIC_BROWSER_RENDER_PROCESS_HOST_OBSERVER_H_
 #define CONTENT_PUBLIC_BROWSER_RENDER_PROCESS_HOST_OBSERVER_H_
 
 #include "base/process/kill.h"
 #include "base/process/process_handle.h"
 #include "content/common/content_export.h"
 
 namespace content {
 
 class RenderProcessHost;
 
 // An observer API implemented by classes which are interested
 // in RenderProcessHost lifecycle events.
 class CONTENT_EXPORT RenderProcessHostObserver {
  public:
+  // This method is invoked when the process is going to exit and should not be
+  // used for further navigations.

[ncarter (slow), 2015/07/21 19:07:15]

I think this gets a little confusing, especially with how RenderProcessExited
has STILL_RUNNING as an option for |status|. So, the more comments here the
better -- in particular, assume that the reader needs to tell the difference
between all the functions here. My mental model is something like:

 - WillExit: don't place any new objects in this renderer process (unless ...
it's recreated???)
 - Exited: you will never again hear from objects that were in this renderer
process (... but watch out, they might be reborn under the same ids in a new
child process!)
 - HostDestroyed: destroy any objects tied to the rph, that aren't tied to the
lifetime of any single child process.

[Avi (use Gerrit), 2015/07/21 20:45:16]

Done.

+  virtual void RenderProcessWillExit(RenderProcessHost* host) {}
+
   // This method is invoked when the process of the observed RenderProcessHost
   // exits (either normally or with a crash). To determine if the process closed
   // normally or crashed, examine the |status| parameter.
   //
   // This will cause a call to WebContentsObserver::RenderProcessGone() for the
   // active renderer process for the top-level frame; for code that needs to be
   // a WebContentsObserver anyway, consider whether that API might be a better
   // choice.
   virtual void RenderProcessExited(RenderProcessHost* host,
                                    base::TerminationStatus status,
                                    int exit_code) {}
 
   // This method is invoked when the observed RenderProcessHost itself is
   // destroyed. This is guaranteed to be the last call made to the observer.
   virtual void RenderProcessHostDestroyed(RenderProcessHost* host) {}
 
  protected:
   virtual ~RenderProcessHostObserver() {}
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_RENDER_PROCESS_HOST_OBSERVER_H_