Introduces AppActivity and handler of chrome.shell API.

athena/content/web_activity.h

Index: athena/content/web_activity.h
diff --git a/athena/content/web_activity.h b/athena/content/web_activity.h
index af012d9f54f307e0ee4d6a5158beb8ac33dc02e1..840cceefb3862f4e5f23f6d8780aada9c2c8309e 100644
--- a/athena/content/web_activity.h
+++ b/athena/content/web_activity.h
@@ -11,6 +11,7 @@
 
 namespace content {
 class BrowserContext;
+class WebContents;
 }
 
 namespace views {
@@ -44,6 +45,7 @@ class WebActivity : public Activity,
 
  private:
   content::BrowserContext* browser_context_;
+  content::WebContents* web_contents_;
   const GURL url_;
   views::WebView* web_view_;