Add keyHintIcon attribute to BaseKeyboard.Key class

This keyHintIcon attribute is used to specify hint icon drawable at
top right corner of Key.

Change-Id: Icaa91e63c4473b2513396bd3fbeb8ed6fd73586c
diff --git a/java/res/values/attrs.xml b/java/res/values/attrs.xml
index 943a43b..1900214 100644
--- a/java/res/values/attrs.xml
+++ b/java/res/values/attrs.xml
@@ -106,8 +106,12 @@
         <attr name="keyOutputText" format="string" />
         <!-- The label to display on the key. -->
         <attr name="keyLabel" format="string" />
+        <!-- The label to display on the key when keyboard is in temporary shift mode. -->
+        <attr name="temporaryShiftKeyLabel" format="string" />
         <!-- The icon to display on the key instead of the label. -->
         <attr name="keyIcon" format="reference" />
+        <!-- The hint icon to display on the key in conjunction with the label -->
+        <attr name="keyHintIcon" format="reference" />
         <!-- Mode of the keyboard. If the mode doesn't match the
              requested keyboard mode, the key will be skipped. -->
         <attr name="keyboardMode" />