[TextBlob] InterceptingCanvas::drawTextBlob() plumbing

Teach InterceptingCanvas & friends about text blobs - otherwise no
drawText calls are shown in Timeline paint recordings when run
with --enable-text-blobs.

BUG=377845
R=caseq@chromium.org,malch@chromium.org,jbroman@chromium.org

Review URL: https://codereview.chromium.org/688083004

git-svn-id: svn://svn.chromium.org/blink/trunk@184952 bbb929c8-8fbe-4397-9dbb-9b2b20218538