Fix to make InputMethodIBus usable on every ChromeOS device (even without TouchUI)

Add switch "--enable-inputmethod-ibus" to enable InputMethodIBus on ChromeOS
Modify gyp files to link IBus

BUG=chromium-os:15566
TEST=manually

Review URL: http://codereview.chromium.org/7004029

git-svn-id: http://src.chromium.org/svn/trunk/src/build@86390 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

common.gypi

@@ -564,7 +564,7 @@
             '<!(<(DEPTH)/tools/clang/scripts/plugin_flags.sh)',
       }],
 
-      # Set 1 to enable ibus support. Currently it is only supported in touchui.
+      # Set use_ibus to 1 to enable ibus support.
       ['touchui==1 and chromeos==1', {
         'use_ibus%': 1,
       }, {