Disable HW BACK key at the incoming-call screen

For devices with HW BACK key, it should be disabled at the incoming-
call screen.  Therefore, a user will not leave the screen by mistake.

Bug: 11548503
Change-Id: I2f4f875c23687afe52a5f816550b9383b9a852c8
diff --git a/src/com/android/incallui/InCallActivity.java b/src/com/android/incallui/InCallActivity.java
index 58db132..64e856c 100644
--- a/src/com/android/incallui/InCallActivity.java
+++ b/src/com/android/incallui/InCallActivity.java
@@ -202,6 +202,13 @@
             return;
         }
 
+        // Always disable the Back key while an incoming call is ringing
+        final Call call = CallList.getInstance().getIncomingCall();
+        if (call != null) {
+            Log.d(this, "Consume Back press for an inconing call");
+            return;
+        }
+
         // Nothing special to do.  Fall back to the default behavior.
         super.onBackPressed();
     }