Let shift globally trigger slow animation mode.

Let shift globally trigger slow animation mode.

A long time ago, we'd used an accelerator to link shift with slow animation
mode, but this affected real key combos so a more piecemeal approach was taken,
disabling/enabling slow animation modes for common ui operations. The problem
with this approach is that it didn't catch many important UI animations. The
fading in and fading out of context menus for example. This CL hooks into the
keyboard event stream at a very high level to enable/disable slow animation
mode. This has its downsides, too -- mainly that we end up with a specific bit
of business littering some very general code.

BUG=None

Review URL: https://chromiumcodereview.appspot.com/11415050

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@168552 0039d316-1c4b-4281-b951-d872f2087c98