Add capability to determine if downgrade to audio is denied.

By default we assume downgrade to audio is permitted; this capability
probides a means for a carrier to specifically deny that.

Bug: 22728624

Change-Id: I75e0a5b9e5ad2d970003a4691b6fc0ac0dcfe9e0
diff --git a/telecomm/java/android/telecom/Connection.java b/telecomm/java/android/telecom/Connection.java
index deb98f4..fa7a59d 100644
--- a/telecomm/java/android/telecom/Connection.java
+++ b/telecomm/java/android/telecom/Connection.java
@@ -255,8 +255,23 @@
      */
     public static final int CAPABILITY_CAN_SEND_RESPONSE_VIA_CONNECTION = 0x00400000;
 
+    /**
+     * When set, prevents a video call from being downgraded to an audio-only call.
+     * <p>
+     * Should be set when the VideoState has the {@link VideoProfile#STATE_TX_ENABLED} or
+     * {@link VideoProfile#STATE_RX_ENABLED} bits set to indicate that the connection cannot be
+     * downgraded from a video call back to a VideoState of
+     * {@link VideoProfile#STATE_AUDIO_ONLY}.
+     * <p>
+     * Intuitively, a call which can be downgraded to audio should also have local and remote
+     * video
+     * capabilities (see {@link #CAPABILITY_SUPPORTS_VT_LOCAL_BIDIRECTIONAL} and
+     * {@link #CAPABILITY_SUPPORTS_VT_REMOTE_BIDIRECTIONAL}).
+     */
+    public static final int CAPABILITY_CANNOT_DOWNGRADE_VIDEO_TO_AUDIO = 0x00800000;
+
     //**********************************************************************************************
-    // Next CAPABILITY value: 0x00800000
+    // Next CAPABILITY value: 0x01000000
     //**********************************************************************************************
 
     /**
@@ -371,6 +386,9 @@
         if (can(capabilities, CAPABILITY_SUPPORTS_VT_REMOTE_BIDIRECTIONAL)) {
             builder.append(" CAPABILITY_SUPPORTS_VT_REMOTE_BIDIRECTIONAL");
         }
+        if (can(capabilities, CAPABILITY_CANNOT_DOWNGRADE_VIDEO_TO_AUDIO)) {
+            builder.append(" CAPABILITY_CANNOT_DOWNGRADE_VIDEO_TO_AUDIO");
+        }
         if (can(capabilities, CAPABILITY_HIGH_DEF_AUDIO)) {
             builder.append(" CAPABILITY_HIGH_DEF_AUDIO");
         }