Disable blink.graphics_context_annotations tracing by default.

Graphics context annotations have a significant impact on recording times and should only be turned on explicitly when needed.

R=pdr@chromium.org
BUG=265015

Review URL: https://chromiumcodereview.appspot.com/21109003

git-svn-id: svn://svn.chromium.org/blink/trunk@155146 bbb929c8-8fbe-4397-9dbb-9b2b20218538