JSObject::DeepCopy and other functions returned an empty handle to
indicate an exception. All usages but one changed to return
MaybeHandles, and to use macros around the call.

The remaining work is in Compiler::GetUnoptimizedCode(), and when
that is turned into a MaybeHandle, then the macros dealing with
null handle returns can be eliminated.

R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/247013002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20877 ce2b1a6d-e550-0410-aec6-3dcde31c8c00