navigation: Retain a screenshot of the page before it unloads

content/browser/web_contents/navigation_entry_impl.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 CONTENT_BROWSER_WEB_CONTENTS_NAVIGATION_ENTRY_IMPL_H_
 #define CONTENT_BROWSER_WEB_CONTENTS_NAVIGATION_ENTRY_IMPL_H_
 
 #include "base/basictypes.h"
 #include "base/memory/ref_counted.h"
 #include "content/browser/site_instance_impl.h"
@@ skipping 149 matching lines @@
   // Whether this (pending) navigation needs to replace current entry.
   // Resets to false after commit.
   bool should_replace_entry() const {
     return should_replace_entry_;
   }
 
   void set_should_replace_entry(bool should_replace_entry) {
     should_replace_entry_ = should_replace_entry;
   }
 
+  void SetScreenshotPNGData(const std::vector<unsigned char>& png_data);

[Charlie Reis, 2012/12/21 23:22:07]

We might be prematurely optimizing with PNG (especially putting it in the
function name).  Your suggestion of capping the amount of space we use might be
sufficient to avoid the encoding/decoding costs, or we might find that WebP is a
better option.

[sadrul, 2012/12/22 00:07:10]

I didn't have optimization in mind when I used the PNG data here :)

We get an SkBitmap from the screenshot callback, and we need to store the data
in a way that can be copied (since NavigationEntryImpl is copy-able) without
much difficulty, and also displayed by the UI code. PNG seemed like a good
choice for this.

+  const scoped_refptr<base::RefCountedBytes> screenshot() const {
+    return screenshot_;
+  }
+
  private:
   // WARNING WARNING WARNING WARNING WARNING WARNING WARNING WARNING WARNING
   // Session/Tab restore save portions of this class so that it can be recreated
   // later. If you add a new field that needs to be persisted you'll have to
   // update SessionService/TabRestoreService and Android WebView
   // state_serializer.cc appropriately.
   // WARNING WARNING WARNING WARNING WARNING WARNING WARNING WARNING WARNING
 
   // See the accessors above for descriptions.
   int unique_id_;
@@ skipping 16 matching lines @@
   GURL original_request_url_;
   bool is_overriding_user_agent_;
   base::Time timestamp_;
 
   // This member is not persisted with session restore because it is transient.
   // If the post request succeeds, this field is cleared since the same
   // information is stored in |content_state_| above. It is also only shallow
   // copied with compiler provided copy constructor.
   scoped_refptr<const base::RefCountedMemory> browser_initiated_post_data_;
 
+  // This is also a transient memeber (i.e. is not persisted with session

[Charlie Reis, 2012/12/21 23:22:07]

typo: memeber

Also, please explain when this screenshot is taken, why it is needed, and why
it's ok for it to be missing.

[sadrul, 2012/12/22 00:07:10]

Done.

+  // restore).
+  scoped_refptr<base::RefCountedBytes> screenshot_;
+
   // This member is not persisted with session restore.
   std::string extra_headers_;
 
   // Used for specifying base URL for pages loaded via data URLs. Only used and
   // persisted by Android WebView.
   GURL base_url_for_data_url_;
 
   // Whether the entry, while loading, was created for a renderer-initiated
   // navigation.  This dictates whether the URL should be displayed before the
   // navigation commits.  It is cleared on commit and not persisted.
@@ skipping 28 matching lines @@
   // Set when this entry should be able to access local file:// resources. This
   // value is not needed after the entry commits and is not persisted.
   bool can_load_local_resources_;
 
   // Copy and assignment is explicitly allowed for this class.
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_WEB_CONTENTS_NAVIGATION_ENTRY_IMPL_H_