Add the LOCAL_EMMA_COVERAGE_FILTER so emma reports make sense

Change-Id: I508c9cd0fd28b275be1ad1183a32c50bd75bda35
diff --git a/Android.mk b/Android.mk
index a6bfd64..9886424 100644
--- a/Android.mk
+++ b/Android.mk
@@ -50,6 +50,8 @@
 
 LOCAL_PROGUARD_FLAG_FILES := proguard.flags
 
+LOCAL_EMMA_COVERAGE_FILTER := +com.android.mail.*
+
 include $(BUILD_PACKAGE)