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/Android.mk b/services/surfaceflinger/Android.mk
index d8152e0..d9bca04 100644
--- a/services/surfaceflinger/Android.mk
+++ b/services/surfaceflinger/Android.mk
@@ -40,6 +40,7 @@
     RenderEngine/Texture.cpp \
     RenderEngine/GLES20RenderEngine.cpp \
     LayerProtoHelper.cpp \
+    RenderArea.cpp \
 
 LOCAL_MODULE := libsurfaceflinger
 LOCAL_C_INCLUDES := \