Add a handle scope to V8Proxy::initContextIfNeeded.
Add a handle scope to V8Proxy::initContextIfNeeded.

initContextIfNeeded can be called without a handle scope in place
which will lead to a renderer crash when creating the first handle.
Also V8Proxy::initContextIfNeeded creates a number of local handles
that should be deallocated on exit.

BUG=8922
Review URL: http://codereview.chromium.org/48131

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@11965 0039d316-1c4b-4281-b951-d872f2087c98

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