GTK: Allow infobubbles to be programtically shrunk.
GTK: Allow infobubbles to be programtically shrunk.

This should only actually affect ExtensionPopups as other infobubbles never resize.

BUG=30294
TEST=chromed bird extension resizes after reverting http://trac.webkit.org/changeset/51492

Review URL: http://codereview.chromium.org/526003

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@35472 0039d316-1c4b-4281-b951-d872f2087c98

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