Cleanup usage of CSSPropertyID and CSSValueID inside Blink.

A lot of call sites were using integers to represent them. While it's
not incorrect per say, it's not ideal for various reason such as type
safety or to remove ambiguity.

This patch eradicate the wrong usage by not letting any integer based
API for getting CSSValueIDs or CSSPropertyIDs from CSSPrimitiveValues.

Instead we use new but typed functions to construct the values as well
as getting them. 2 custom and internal types were added to CSSPrimitiveValue
to handle correctly the new APIs.

It's good to note that in order to preserve compatibility on the
CSSPrimitiveValue type whenever CSSPrimitiveValue handles a CSSValueID
or a CSSPropertyID the return type for the public API will be CSS_IDENT
despite it is a separate internal type.

Review URL: https://chromiumcodereview.appspot.com/16415007

git-svn-id: svn://svn.chromium.org/blink/trunk@151975 bbb929c8-8fbe-4397-9dbb-9b2b20218538
42 files changed