Clean up physical coupling

Narrow the use of #include directives in hwui, replacing with forward
declarations where straightforward. Speeds compiles; doesn't do any
restructuring of code.

Change-Id: Icac2baffb5896f55d8c6718e9bd9d4bfa02d3ca0
diff --git a/libs/hwui/AmbientShadow.h b/libs/hwui/AmbientShadow.h
index 9660dc0..8eb1048 100644
--- a/libs/hwui/AmbientShadow.h
+++ b/libs/hwui/AmbientShadow.h
@@ -19,13 +19,13 @@
 #define ANDROID_HWUI_AMBIENT_SHADOW_H
 
 #include "Debug.h"
-#include "OpenGLRenderer.h"
 #include "Vector.h"
-#include "VertexBuffer.h"
 
 namespace android {
 namespace uirenderer {
 
+class VertexBuffer;
+
 /**
  * AmbientShadow is used to calculate the ambient shadow value around a polygon.
  */