Avoid re-parsing of string in fillText and measureText calls of Canvas 2D.

Allowing "width" method in Font.cpp to handle space normalization.

R=eae@chromium.org
BUG=413225
TEST=fast/canvas/canvas-normalize-string.html

Review URL: https://codereview.chromium.org/567543002

git-svn-id: svn://svn.chromium.org/blink/trunk@182675 bbb929c8-8fbe-4397-9dbb-9b2b20218538