Add a LayerScreenshot

A LayerScreenshot is a special type of layer that contains a screenshot of
the screen acquired when its created. It works just like LayerDim.

Make sure to call compositionComplete() after rendering into a FBO.

Bug: 5446982, 5467587, 5466259
Change-Id: I5d8a1b4c327f9973d950cd4f4c0bca7f62825cd4

core/java/android/view/Surface.java

@@ -194,6 +194,9 @@ public class Surface implements Parcelable {
      */
     public static final int FX_SURFACE_DIM     = 0x00020000;
 
+    /** @hide */
+    public static final int FX_SURFACE_SCREENSHOT   = 0x00030000;
+
     /** Mask used for FX values above @hide */
     public static final int FX_SURFACE_MASK     = 0x000F0000;