Restrict access to instant app data in usage stats

- Events are obfuscated based on whether the app was instant or not at
the time each event was logged.

- UsageStats are obfuscated based on whether each app is instant or
not at the moment.

Bug 38202133
Test: Manual test using UsageStatsTest and instant apps

Change-Id: I3c74309196b88d010d317cb0dd6749bf4624e876
diff --git a/tests/UsageStatsTest/Android.mk b/tests/UsageStatsTest/Android.mk
index 5f7467a..6b5c999 100644
--- a/tests/UsageStatsTest/Android.mk
+++ b/tests/UsageStatsTest/Android.mk
@@ -8,6 +8,8 @@
 
 LOCAL_STATIC_JAVA_LIBRARIES := android-support-v4
 
+LOCAL_CERTIFICATE := platform
+
 LOCAL_PACKAGE_NAME := UsageStatsTest
 
 include $(BUILD_PACKAGE)