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

chrome/browser/extensions/extension_host.h

Index: chrome/browser/extensions/extension_host.h
diff --git a/chrome/browser/extensions/extension_host.h b/chrome/browser/extensions/extension_host.h
index ede9387037e4ac727eeef25c7e803097172ef934..ed94325845bad220c80faaf84a8bb99a34fba1ce 100644
--- a/chrome/browser/extensions/extension_host.h
+++ b/chrome/browser/extensions/extension_host.h
@@ -52,6 +52,19 @@ class ExtensionHost : public content::WebContentsDelegate,
                       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)
@@ -65,7 +78,9 @@ class ExtensionHost : public content::WebContentsDelegate,
   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();
@@ -219,6 +234,9 @@ class ExtensionHost : public content::WebContentsDelegate,
   // 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_;