Secure windows, secure surface views and secure displays.

Add new API to determine whether a display is secure.
Add new API to make a SurfaceView secure.
Clarify documentation.

Bug: 7368436
Change-Id: I7068c34c910e43b4bc72e43fa0dded59a25f0fe2
diff --git a/services/java/com/android/server/display/LogicalDisplay.java b/services/java/com/android/server/display/LogicalDisplay.java
index aa7ea82..aa62aee 100644
--- a/services/java/com/android/server/display/LogicalDisplay.java
+++ b/services/java/com/android/server/display/LogicalDisplay.java
@@ -186,6 +186,9 @@
             if ((deviceInfo.flags & DisplayDeviceInfo.FLAG_SUPPORTS_PROTECTED_BUFFERS) != 0) {
                 mBaseDisplayInfo.flags |= Display.FLAG_SUPPORTS_PROTECTED_BUFFERS;
             }
+            if ((deviceInfo.flags & DisplayDeviceInfo.FLAG_SECURE) != 0) {
+                mBaseDisplayInfo.flags |= Display.FLAG_SECURE;
+            }
             mBaseDisplayInfo.name = deviceInfo.name;
             mBaseDisplayInfo.appWidth = deviceInfo.width;
             mBaseDisplayInfo.appHeight = deviceInfo.height;