Added Shift-Reload support for Mac.
Added Shift-Reload support for Mac.

On Mac, holding down shift while pressing the reload button now reloads the
page ignoring any caches.

Command-Shift-R doesn't do anything, just like in Safari.

BUG=36245
TEST=visit astronomy picture of the day; hit reload, picture pops
up quickly; hit shift-reload, picture loads slowly

Review URL: http://codereview.chromium.org/651033

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@39444 0039d316-1c4b-4281-b951-d872f2087c98

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