[wip] Introduce SiteInstanceKeepAlive.

content/browser/frame_host/navigation_entry_screenshot_manager.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_BROWSER_FRAME_HOST_NAVIGATION_ENTRY_SCREENSHOT_MANAGER_H_
 #define CONTENT_BROWSER_FRAME_HOST_NAVIGATION_ENTRY_SCREENSHOT_MANAGER_H_
 
 #include "base/compiler_specific.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/scoped_vector.h"
 #include "base/memory/weak_ptr.h"
 #include "base/time/time.h"
 #include "content/common/content_export.h"
+#include "content/public/browser/web_contents_observer.h"
 
 class SkBitmap;
 
 namespace content {
 
 class NavigationControllerImpl;
 class NavigationEntryImpl;
 class RenderViewHost;
 class ScreenshotData;
+class SiteInstanceKeepAlive;
 
 // NavigationEntryScreenshotManager takes care of taking image-captures for the
 // current navigation entry of a NavigationControllerImpl, and managing these
 // captured images. These image-captures are used for history navigation using
 // overscroll gestures.
-class CONTENT_EXPORT NavigationEntryScreenshotManager {
+class CONTENT_EXPORT NavigationEntryScreenshotManager
+    : public WebContentsObserver {
  public:
   explicit NavigationEntryScreenshotManager(
       NavigationControllerImpl* controller);
   virtual ~NavigationEntryScreenshotManager();
 
   // Takes a screenshot of the last-committed entry of the controller.
   void TakeScreenshot();
 
   // Clears screenshots of all navigation entries.
   void ClearAllScreenshots();
 
  protected:
   virtual void TakeScreenshotImpl(RenderViewHost* host,
                                   NavigationEntryImpl* entry);
 
   // Called after a screenshot has been set on an NavigationEntryImpl.
   // Overridden in tests to get notified of when a screenshot is set.
   virtual void OnScreenshotSet(NavigationEntryImpl* entry);
 
   NavigationControllerImpl* owner() { return owner_; }
 
   void SetMinScreenshotIntervalMS(int interval_ms);
 
   // The callback invoked when taking the screenshot of the page is complete.
   // This sets the screenshot on the navigation entry.
   void OnScreenshotTaken(int unique_id,
+                         SiteInstanceKeepAlive* keep_alive,
                          bool success,
                          const SkBitmap& bitmap);
 
   // Returns the number of entries with screenshots.
   int GetScreenshotCount() const;
 
  private:
   // This is called when the screenshot data has beene encoded to PNG in a
   // worker thread.
   void OnScreenshotEncodeComplete(int unique_id,
                                   scoped_refptr<ScreenshotData> data);
 
   // Removes the screenshot for the entry, returning true if the entry had a
   // screenshot.
   bool ClearScreenshot(NavigationEntryImpl* entry);
 
   // The screenshots in the NavigationEntryImpls can accumulate and consume a
   // large amount of memory. This function makes sure that the memory
   // consumption is within a certain limit.
   void PurgeScreenshotsIfNecessary();
 
+  // WebContentsObserver:
+  virtual void WebContentsDestroyed(WebContents* contents) OVERRIDE;
+
   // The navigation controller that owns this screenshot-manager.
   NavigationControllerImpl* owner_;
 
+  // Keeps track of (and owns) all the SiteInstanceKeepAlive objects created for
+  // screenshot requests.
+  ScopedVector<SiteInstanceKeepAlive> keep_alives_;
+
   // Taking a screenshot and encoding them can be async. So use a weakptr for
   // the callback to make sure that the screenshot/encoding completion callback
   // does not trigger on a destroyed NavigationEntryScreenshotManager.
   base::WeakPtrFactory<NavigationEntryScreenshotManager> screenshot_factory_;
 
   base::Time last_screenshot_time_;
   int min_screenshot_interval_ms_;
 
   DISALLOW_COPY_AND_ASSIGN(NavigationEntryScreenshotManager);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_FRAME_HOST_NAVIGATION_ENTRY_SCREENSHOT_MANAGER_H_