Data Usage public API

Added new API consisting of android.app.usage.NetworkUsageManager and
android.app.usage.NetworkUsageStats. Through them data usage on a
network interface can be programmatically queried. Both summary and
details are available.

Bug: 19208876
Change-Id: I0e0c4b37ae23ad1e589d4b0c955b93f28ba4333e
diff --git a/core/res/AndroidManifest.xml b/core/res/AndroidManifest.xml
index 4d6b5f6..5421ee4 100644
--- a/core/res/AndroidManifest.xml
+++ b/core/res/AndroidManifest.xml
@@ -2607,7 +2607,8 @@
         android:protectionLevel="signature|system" />
 
     <!-- @SystemApi Allows an application to collect component usage
-         statistics @hide -->
+         statistics
+         <p>Not for use by third-party applications. -->
     <permission android:name="android.permission.PACKAGE_USAGE_STATS"
         android:label="@string/permlab_pkgUsageStats"
         android:description="@string/permdesc_pkgUsageStats"