BUILD FIX (r143637): Export ScriptController::javaScriptContext() on iOS
<http://webkit.org/b/106059>

Fixes the following build failure:

    Undefined symbols for architecture armv7:
      "__ZN7WebCore16ScriptController17javaScriptContextEv", referenced from:
          -[WebFrame javaScriptContext] in WebFrame.o
          __ZN20WebFrameLoaderClient35dispatchDidClearWindowObjectInWorldEPN7WebCore15DOMWrapperWorldE in WebFrameLoaderClient.o
    ld: symbol(s) not found for architecture armv7

* WebCore.exp.in: Export ScriptController::javaScriptContext()
even more unconditionally.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@144546 268f45cc-cd09-0410-ab3c-d52691b4dbfc