Code clean up, changing bool to Enum type for better code readability and some optimizations.
(This is in reference to comments received in other patch)

 Patch handles following two cases:
1. Replace int with CSSValueID
2. Use new Enum in place of "bool shouldUseFixedDefaultSize"
3. Few Optimizations

Review URL: https://codereview.chromium.org/342883004

git-svn-id: svn://svn.chromium.org/blink/trunk@177314 bbb929c8-8fbe-4397-9dbb-9b2b20218538