Change various helper classes to transition types to get CSSValue entirely onto the gc heap.

Source/core/css/CSSGrammar.y

Index: Source/core/css/CSSGrammar.y
diff --git a/Source/core/css/CSSGrammar.y b/Source/core/css/CSSGrammar.y
index 65c24613abe1b07027e56cbd26936cae5ba40c44..47f20d398350853ca70c8056dfcc8f6dc14fb515 100644
--- a/Source/core/css/CSSGrammar.y
+++ b/Source/core/css/CSSGrammar.y
@@ -85,7 +85,7 @@ using namespace HTMLNames;
     MediaQueryExp* mediaQueryExp;
     CSSParserValue value;
     CSSParserValueList* valueList;
-    Vector<OwnPtr<MediaQueryExp> >* mediaQueryExpList;
+    WillBeHeapVector<OwnPtrWillBeMember<MediaQueryExp> >* mediaQueryExpList;

[Mads Ager (chromium), 2014/03/03 11:30:21]

As with the ruleList above, I guess there is something else in the
BisonCSSParser that is keeping these alive? Add a comment or group these
together with a common comment?

[wibling-chromium, 2014/03/03 11:40:17]

I will group it with the above StyleRuleBase vector. It is a bit unfortunate
that we have these, but I am not sure how to better fix it.

     StyleKeyframe* keyframe;
     Vector<RefPtr<StyleKeyframe> >* keyframeRuleList;
     float val;