Mac: Add a few more keyboard shortcuts to tabpose.
Mac: Add a few more keyboard shortcuts to tabpose.

* shift / tab-shift cycle through all open tabs
* arrow keys move selection up, down, left, right
* cmd-1-8 selects tab 1-8 and exits tabpose, cmd-9 selects last tab and exits tabpose
* cmd-ctrl-t exits tabpose

BUG=50307,55530
TEST=try it

Review URL: http://codereview.chromium.org/3389010

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@59703 0039d316-1c4b-4281-b951-d872f2087c98

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