Issue #80- De-unify gfx/layers

Excludes layers/ipc/CompositorBridgeParent and CrossProcessCompositorBridgeParent
because the latter purposely uses functions implemented in the former.
See also code comment in CrossProcessCompositorBridgeParent.cpp

Note: likely dead code for us anyway; likely not worth investing in to solve.

gfx/layers/client/ClientCanvasLayer.cpp

@@ -19,6 +19,9 @@
 #include "nsRect.h"                     // for mozilla::gfx::IntRect
 #include "nsXULAppAPI.h"                // for XRE_GetProcessType, etc
 #include "gfxPrefs.h"                   // for WebGLForceLayersReadback
+#include "gfxUtils.h"
+#include "TextureClientSharedSurface.h"
+
 
 using namespace mozilla::gfx;
 using namespace mozilla::gl;