Speed up jsStringWithCache() through WeakGCMap inlining.
<https://webkit.org/b/131923>

Source/JavaScriptCore:
Always inline WeakGCMap::add() but move the slow garbage collecting
path out-of-line.

Reviewed by Darin Adler.

* runtime/WeakGCMap.h:
(JSC::WeakGCMap::add):
(JSC::WeakGCMap::gcMap):

Source/WebCore:
Inline the common path of WeakGCMap::add() in jsStringWithCache().
26% progression on Bindings/id-getter.html

Reviewed by Darin Adler.

* WebCore.exp.in:
* bindings/js/JSDOMBinding.h:
* bindings/js/JSDOMBinding.cpp:
(WebCore::jsStringWithCache):

    Move jsStringWithCache() out of line since we're now blowing up
    its size quite a bit.

Source/WTF:
Add HashMap::fastAdd(), which is the same as add() except we'll tell
the compiler to aggressively inline it.

Reviewed by Darin Adler.

* wtf/HashMap.h:
* wtf/HashTable.h:


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@167577 268f45cc-cd09-0410-ab3c-d52691b4dbfc