A Chrome-side fix for Issue 18232. This change enables the code which displays a context menu when Chrome receives a key event for a menu key or control+F10 keys also on Linux. Even though this change makes Chrome display a context menu when we type control+F10 keys, it cannot make Chrome display a context menu when we type a menu key because WebKit maps a GDK_Menu to a VKEY_MENU. To fix this problem, we need to change WebKit to map a GDK_Menu to a VKEY_APP. 
A Chrome-side fix for Issue 18232.
This change enables the code which displays a context menu when Chrome receives a key event for a menu key or control+F10 keys also on Linux. Even though this change makes Chrome display a context menu when we type control+F10 keys, it cannot make Chrome display a context menu when we type a menu key because WebKit maps a GDK_Menu to a VKEY_MENU. To fix this problem, we need to change WebKit to map a GDK_Menu to a VKEY_APP. 

BUG=18232 "[Linux] Menu key doesn't work"
TEST=Press a menu key (or control+F10 keys), and verify a context menu is displayed.
Review URL: http://codereview.chromium.org/164131

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@22910 0039d316-1c4b-4281-b951-d872f2087c98

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