Make start/stop loading notifications per-frame

Also, make ProgressTracker a frame-level concept rather than a page-level concept and merge it with FrameLoader's FrameProgressTracker helper. Send per-frame progress change notifications accordingly.

This depends on https://codereview.chromium.org/180113003/ landing in chromium.

BUG=347643

Review URL: https://codereview.chromium.org/183793002

git-svn-id: svn://svn.chromium.org/blink/trunk@170192 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Change the BMP decoder to not reject paletted images which use color indexes
beyond the end of the color table.  Instead, draw these pixels as black.

This matches Firefox and IE.

BUG=176678
TEST=none
R=abarth@chromium.org, hclam@chromium.org

Review URL: https://codereview.chromium.org/213613002

git-svn-id: svn://svn.chromium.org/blink/trunk@170193 bbb929c8-8fbe-4397-9dbb-9b2b20218538