Remove calls to deprecated toWebCoreStringWithNullCheck(v8::Handle<v8::Value>)

Remove calls to deprecated toWebCoreStringWithNullCheck(v8::Handle<v8::Value>) and
use the V8TRYCATCH_FOR_V8STRINGRESOURCE*() macros instead so that we return early
if an exception is thrown by v8::String::ToString().

R=haraken
BUG=327338

Review URL: https://codereview.chromium.org/110633002

git-svn-id: svn://svn.chromium.org/blink/trunk@163708 bbb929c8-8fbe-4397-9dbb-9b2b20218538