DevTools: add LazyPixelRef id to ImageDecodeTask event

... so we can relate ImageDecode events to image element reference and
resource URL.
Related blink change: https://codereview.chromium.org/24096002

BUG=
R=ernstm@chromium.org, nduca@chromium.org

Review URL: https://codereview.chromium.org/23537033

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@224691 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 224691