Add captive portal API.

This API allows apps other than the system's CaptivePortalLogin
to handle signing in to captive portals.

bug:19416463
Change-Id: I27fce5856b635233e6ff66396d50ccabedd76cf5
diff --git a/core/res/AndroidManifest.xml b/core/res/AndroidManifest.xml
index b1213b3..ed21e80 100644
--- a/core/res/AndroidManifest.xml
+++ b/core/res/AndroidManifest.xml
@@ -208,6 +208,7 @@
     <protected-broadcast android:name="android.intent.action.MEDIA_UNMOUNTABLE" />
     <protected-broadcast android:name="android.intent.action.MEDIA_EJECT" />
 
+    <protected-broadcast android:name="android.net.conn.CAPTIVE_PORTAL" />
     <protected-broadcast android:name="android.net.conn.CONNECTIVITY_CHANGE" />
     <protected-broadcast android:name="android.net.conn.CONNECTIVITY_CHANGE_IMMEDIATE" />
     <protected-broadcast android:name="android.net.conn.DATA_ACTIVITY_CHANGE" />