Add captureLayers function to capture a layer and its children.

The captureLayers function gets a root layer as its argument.
It will capture the content for that layer and its descendants. The
capture will set the root layer's transform back to (0, 0).

Test: Transaction_test ScreenCaptureTest
Change-Id: I84fb66a65cd91434cddc99506b1924cf9f950935
diff --git a/services/surfaceflinger/Transform.h b/services/surfaceflinger/Transform.h
index 6640a13..bfc66ec 100644
--- a/services/surfaceflinger/Transform.h
+++ b/services/surfaceflinger/Transform.h
@@ -25,6 +25,8 @@
 #include <math/vec2.h>
 #include <math/vec3.h>
 
+#include <gui/ISurfaceComposer.h>
+
 #include <hardware/hardware.h>
 
 namespace android {
@@ -51,6 +53,8 @@
                 ROT_INVALID = 0x80
             };
 
+            static orientation_flags fromRotation(ISurfaceComposer::Rotation rotation);
+
             enum type_mask {
                 IDENTITY            = 0,
                 TRANSLATE           = 0x1,