Replacing home page buckets icon

This was in svg and so we couldn't see it; this replaces it with a png version.

Review URL: https://codereview.chromium.org/147053002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246973 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 246973
Cast: Fix threading issues in VideoEncoderImpl

VideoEncoderImpl can be used after delete. We assumed that main thread
out-live video encoder thread. This is not true for some use cases. For
example in the renderer when video encoder thread is shared by multiple
instances of CastSEnder. To fix this we need to separate Vp8Encoder and
VideoEncoderImpl.

VideoEncoderImpl will live on the main thread only. And Vp8Encoder will
live on the video encoder thread only.

Tested this change with vagrind and cast_unittests reports no error.

TBR=mikhal@chromium.org
BUG=336887

Review URL: https://codereview.chromium.org/138953009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246974 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 246974