TextAutosizer: avoid unnecessary calls to containerShouldBeAutosized.

This patch adds a simple check to ensure that the multiplier > 1
before calling containerShouldBeAutosized() inside processContainer().
If the multiplier is exactly 1 the return value of
containerShouldBeAutosized does not matter. Due to the cascading
structure of the algorithm quite a few unnecessary calls to
containerShouldBeAutosized are avoided in this way, reducing the text
autosizing times by up to 30% on some websites.

Reduction of measured time spent in text autosizing (in %):
amazon.co.uk - 17%
www.nytimes.com - 27%
www.answers.com - 31%
www.yahoo.com - 16%
http://en.wikipedia.org/wiki/Cat - 9%

BUG=

Review URL: https://codereview.chromium.org/134153006

git-svn-id: svn://svn.chromium.org/blink/trunk@165479 bbb929c8-8fbe-4397-9dbb-9b2b20218538