Generate thumbnails in the browser process.

The feature is now behind --enable-in-browser-thumbnailing flag.

The in-browser thumbnailing works as follows:

- The scroll offset is sent from the renderer to the browser.
- The thumbnail is taken when the page info is sent from the renderer process.
- Since thumbnails are generated in the browser, we can avoid the generation when unnecessary (ex. off-the-record mode, or New Tab Page).
- The quality of thumbnails is as good as before, as the patch doesn't change timing heuristics.
- The drawback is that we cannot take thumbnails from background tabs.

New functions are added to ThumbnailGenerator for clipping thumbnails, with tests.

BUG=65936
TEST=add unit tests for thumbnail_generator. confirmed that the thumbnails are updated with and without --enable-in-browser-thumbnailing

Review URL: http://codereview.chromium.org/6246007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@72115 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 4 insertions, 0 deletions

diff --git a/chrome/renderer/render_widget.h b/chrome/renderer/render_widget.h
index 33d0205..71a065e 100644
--- a/chrome/renderer/render_widget.h
+++ b/chrome/renderer/render_widget.h
@@ -219,6 +219,10 @@ class RenderWidget : public IPC::Channel::Listener,
       gfx::Rect* location,
       gfx::Rect* clip);
 
+  // Gets the scroll offset of this widget, if this widget has a notion of
+  // scroll offset.
+  virtual gfx::Size GetScrollOffset();
+
   // Sets the "hidden" state of this widget.  All accesses to is_hidden_ should
   // use this method so that we can properly inform the RenderThread of our
   // state.