Use Vector::reserveInitialCapacity and Vector::uncheckedAppend for JSC's APIs
https://bugs.webkit.org/show_bug.cgi?id=113651

Reviewed by Andreas Kling.

This removes a bunch of branches on initialization and when
filling the vector.

* API/JSCallbackConstructor.cpp:
(JSC::constructJSCallback):
* API/JSCallbackFunction.cpp:
(JSC::JSCallbackFunction::call):
* API/JSCallbackObjectFunctions.h:
(JSC::::construct):
(JSC::::call):
* API/JSObjectRef.cpp:
(JSObjectCopyPropertyNames):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@147349 268f45cc-cd09-0410-ab3c-d52691b4dbfc