DevTools: [CanvasProfiler] Implement CanvasAgent.getResourceState in the backend for WebGL objects.

This patch was extracted from https://codereview.chromium.org/19948003/

BUG=253854
R=pfeldman@chromium.org

Review URL: https://codereview.chromium.org/22816003

git-svn-id: svn://svn.chromium.org/blink/trunk@156003 bbb929c8-8fbe-4397-9dbb-9b2b20218538