Move StylePropertySet::createImmutable() to ImmutableStylePropertySet.

StylePropertySet::createImmutable() -> ImmutableStylePropertySet::create()
Also, immutableCopyIfNeeded() now returns a PassRefPtr<ImmutableStylePropertySet>.

This is a backport from WebKit r148398. Patch by Andreas Kling reviewed by Anders Carlsson.

R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/16021003

git-svn-id: svn://svn.chromium.org/blink/trunk@151124 bbb929c8-8fbe-4397-9dbb-9b2b20218538
3 files changed