Add boolean resource isDefault=true for all supported locales

Bug: 7115368
Change-Id: I390d52d10d6c7d1639f73255ace9985886ea2157
diff --git a/java/res/values-en/bools.xml b/java/res/values-en/bools.xml
index dabfff8..c289e5b 100644
--- a/java/res/values-en/bools.xml
+++ b/java/res/values-en/bools.xml
@@ -18,5 +18,7 @@
 */
 -->
 <resources>
+    <!-- Whether this input method should be used as the default for a locale. Override it
+         for supported languages. -->
     <bool name="im_is_default">true</bool>
 </resources>