gtk: Desensitize the "End Process" button when first loading the task manager.
gtk: Desensitize the "End Process" button when first loading the task manager.

BUG=18582
TEST=Open the task manager.  The "End Process" button should not be sensitive.
Review URL: http://codereview.chromium.org/164261

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@22930 0039d316-1c4b-4281-b951-d872f2087c98

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