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/ResourceCache.h b/libs/hwui/ResourceCache.h
index 3864d4b..c43a056 100644
--- a/libs/hwui/ResourceCache.h
+++ b/libs/hwui/ResourceCache.h
@@ -20,16 +20,17 @@
 #include <cutils/compiler.h>
 
 #include <SkBitmap.h>
+#include <SkPath.h>
 
 #include <utils/KeyedVector.h>
 
 #include <androidfw/ResourceTypes.h>
 
-#include "Layer.h"
-
 namespace android {
 namespace uirenderer {
 
+class Layer;
+
 /**
  * Type of Resource being cached
  */