Add inspector node id to GraphicsContextAnnotation

This adds a AnnotateInspectorIds to AnnotationModeFlag. When it's set,
the annotation will include stringized inspector node id, so that we
can expose nodes in Timeline's paint profiler.

BUG=

Review URL: https://codereview.chromium.org/373053002

git-svn-id: svn://svn.chromium.org/blink/trunk@177677 bbb929c8-8fbe-4397-9dbb-9b2b20218538