Make popup hint letter theme-aware

Bug: 16351091
Change-Id: I6af18ea210c00916157138b9cfbeb073aee6ca1b
diff --git a/java/res/values/attrs.xml b/java/res/values/attrs.xml
index 003b011..9a22273 100644
--- a/java/res/values/attrs.xml
+++ b/java/res/values/attrs.xml
@@ -52,7 +52,9 @@
         <attr name="spacebarIconWidthRatio" format="float" />
         <!-- Right padding of hint letter to the edge of the key.-->
         <attr name="keyHintLetterPadding" format="dimension" />
-        <!-- Bottom padding of popup hint letter "..." to the edge of the key.-->
+        <!-- Popup hint letter string-->
+        <attr name="keyPopupHintLetter" format="string" />
+        <!-- Bottom padding of popup hint letter to the edge of the key.-->
         <attr name="keyPopupHintLetterPadding" format="dimension" />
         <!-- Right padding of shifted letter hint to the edge of the key.-->
         <attr name="keyShiftedLetterHintPadding" format="dimension" />