install dialogs and the management ui page.

Also changed the margins on the body to match the download page and
the history page so it doesn't look as bad when you switch between them.

TEST=Install an extension without an icon and you should see the puzzle
piece icon in the install dialog.
TEST=Open the chrome://extensions page and you should see the same icon
in the top left corner.
BUG=25906

Review URL: http://codereview.chromium.org/344014

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@30384 0039d316-1c4b-4281-b951-d872f2087c98