Add WebRuntimeFeatures::enableImageColorProfiles

Add a run-time feature enableImageColorProfiles, default off, to be
plumbed from a Chromium-side commandline flag:

 https://codereview.chromium.org/658683003

BUG=423670, 369787

Review URL: https://codereview.chromium.org/646033003

git-svn-id: svn://svn.chromium.org/blink/trunk@183762 bbb929c8-8fbe-4397-9dbb-9b2b20218538