Keep browser process alive while there are platform apps with background pages running.

chrome/browser/extensions/extension_host.h

 // Copyright (c) 2012 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 CHROME_BROWSER_EXTENSIONS_EXTENSION_HOST_H_
 #define CHROME_BROWSER_EXTENSIONS_EXTENSION_HOST_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 34 matching lines @@
 
 // This class is the browser component of an extension component's RenderView.
 // It handles setting up the renderer process, if needed, with special
 // privileges available to extensions.  It may have a view to be shown in the
 // browser UI, or it may be hidden.
 class ExtensionHost : public content::WebContentsDelegate,
                       public content::WebContentsObserver,
                       public ExtensionFunctionDispatcher::Delegate,
                       public content::NotificationObserver {
  public:
+  // Any behavior that is different for different types of background hosts
+  // should go in ExtensionHost::Delegate. ExtensionHost::Delegate is not
+  // abstract, this class provides the default behavior.
+  class Delegate {

[Yoyo Zhou, 2012/10/30 01:35:22]

As we discussed, this delegate feels like more complexity than it's worth. Also,
I'm not confident that "delegate" is really the right name for this. It seems
easier to subclass ExtensionHost, overriding KeepsBrowserProcessAlive.

This may change later if you want to have more different behaviors for platform
app hosts, but as it is, you could pass a bool instead of a Delegate to the
constructor and achieve the same effect.

I'll let Aaron comment on this also.

[benwells, 2012/10/30 02:55:23]

I agree with your comments. I don't like passing the bool in as it just moves
the platform app specific behavior down to ExtensionProcessManager, where it
belongs even less.

A better approach would be to add a PlatformAppService which listens to
EXTENSION_HOST_CREATED and EXTENSION_HOST_DESTROYED messages. That shouldn't
have any of these problems, and would be a natural place for the
ShellWindowRegistry to live.

I'll see how that feels later today, if I get to it.

[Aaron Boodman, 2012/10/30 05:30:08]

This sounds like a good plan to me!

+   public:
+    Delegate() {}
+    virtual ~Delegate() {}
+
+    // True if the browser process should be kept alive while this extension
+    // host is active.
+    virtual bool KeepsBrowserProcessAlive();
+  };
+
   class ProcessCreationQueue;
 
 #if defined(TOOLKIT_VIEWS)
   typedef ExtensionViewViews PlatformExtensionView;
 #elif defined(OS_MACOSX)
   typedef ExtensionViewMac PlatformExtensionView;
 #elif defined(TOOLKIT_GTK)
   typedef ExtensionViewGtk PlatformExtensionView;
 #elif defined(OS_ANDROID)
   // Android does not support extensions.
   typedef ExtensionViewAndroid PlatformExtensionView;
 #endif
 
+  // The ExtensionHost will take ownership of |delegate|.
   ExtensionHost(const Extension* extension,
+                Delegate* delegate,
                 content::SiteInstance* site_instance,
                 const GURL& url, chrome::ViewType host_type);
   virtual ~ExtensionHost();
 
 #if defined(TOOLKIT_VIEWS)
   void set_view(PlatformExtensionView* view) { view_.reset(view); }
 #endif
 
   const PlatformExtensionView* view() const {
 #if defined(OS_ANDROID)
@@ skipping 133 matching lines @@
 
   // The extension that we're hosting in this view.
   const Extension* extension_;
 
   // Id of extension that we're hosting in this view.
   const std::string extension_id_;
 
   // The profile that this host is tied to.
   Profile* profile_;
 
+  // The delegate for this host.
+  scoped_ptr<Delegate> delegate_;
+
   // Optional view that shows the rendered content in the UI.
   scoped_ptr<PlatformExtensionView> view_;
 
   // Used to create dialog boxes.
   // It must outlive host_contents_ as host_contents_ will access it
   // during destruction.
   scoped_ptr<content::JavaScriptDialogCreator> dialog_creator_;
 
   // The host for our HTML content.
   scoped_ptr<content::WebContents> host_contents_;
@@ skipping 24 matching lines @@
 
   // Used to measure how long it's been since the host was created.
   PerfTimer since_created_;
 
   DISALLOW_COPY_AND_ASSIGN(ExtensionHost);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_EXTENSION_HOST_H_