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
diff --git a/include/surfaceflinger/ISurfaceComposer.h b/include/surfaceflinger/ISurfaceComposer.h
index ea022a6..e7a33f1 100644
--- a/include/surfaceflinger/ISurfaceComposer.h
+++ b/include/surfaceflinger/ISurfaceComposer.h
@@ -53,6 +53,7 @@
         eFXSurfaceNormal    = 0x00000000,
         eFXSurfaceBlur      = 0x00010000,
         eFXSurfaceDim       = 0x00020000,
+        eFXSurfaceScreenshot= 0x00030000,
         eFXSurfaceMask      = 0x000F0000,
     };