Change SkCanvasState to use inheritance.

include/utils/SkCanvasStateUtils.h

Index: include/utils/SkCanvasStateUtils.h
diff --git a/include/utils/SkCanvasStateUtils.h b/include/utils/SkCanvasStateUtils.h
index f8266c9b324ce753d5087300cc2b89360b8fad18..6ea7b10307439ab285d2a97e1a13a51dbf77c697 100644
--- a/include/utils/SkCanvasStateUtils.h
+++ b/include/utils/SkCanvasStateUtils.h
@@ -13,9 +13,9 @@
 class SkCanvasState;
 
 /**
- * A set of functions that are useful for copying an SkCanvas across a library
- * boundary where the Skia libraries on either side of the boundary may not be
- * version identical.  The expected usage is outline below...
+ * A set of functions that are useful for copying the state of an SkCanvas
+ * across a library boundary where the Skia library on the other side of the
+ * boundary may be newer. The expected usage is outline below...
  *
  *                          Lib Boundary
  * CaptureCanvasState(...)      |||
@@ -30,8 +30,8 @@ class SkCanvasState;
 namespace SkCanvasStateUtils {
     /**
      * Captures the current state of the canvas into an opaque ptr that is safe
-     * to pass between different instances of Skia (which may or may not be the
-     * same version). The function will return NULL in the event that one of the
+     * to pass to a different instance of Skia (which may be the same version,
+     * or may be newer). The function will return NULL in the event that one of the
      * following conditions are true.
      *  1) the canvas device type is not supported (currently only raster is supported)
      *  2) the canvas clip type is not supported (currently only non-AA clips are supported)
@@ -56,7 +56,7 @@ namespace SkCanvasStateUtils {
      *  1) the captured state is in an unrecognized format
      *  2) the captured canvas device type is not supported
      *
-     * @param canvas The canvas you wish to capture the current state of.
+     * @param state Opaque object created by CaptureCanvasState.
      * @return NULL or an SkCanvas* whose devices and matrix/clip state are
      *         identical to the captured canvas. The caller is responsible for
      *         calling unref on the SkCanvas.
@@ -66,7 +66,8 @@ namespace SkCanvasStateUtils {
     /**
      * Free the memory associated with the captured canvas state.  The state
      * should not be released until all SkCanvas objects created using that
-     * state have been dereferenced.
+     * state have been dereferenced. Must be called from the same library
+     * instance that created the state via CaptureCanvasState.
      *
      * @param state The captured state you wish to dispose of.
      */