FlameChart: Speed up flamechart draw procedure. Reduce the number of fillStyle calls.

On the huge profiles flame chart has to draw number of bars.
Each bar requires 2  calls to the context.fillStyle.
One for color of the current bar and the other for color of the text.
I reduced the number of calls to the context.fillStyle  with help of
splitting the procedure on two parts. One for drawing bars
and the other for drawing texts.

BUG=none
R=yurys@chromium.org

Review URL: https://codereview.chromium.org/23570007

git-svn-id: svn://svn.chromium.org/blink/trunk@157203 bbb929c8-8fbe-4397-9dbb-9b2b20218538