Make GrReducedClip's gen ID only apply to the element list

src/gpu/GrReducedClip.h

Index: src/gpu/GrReducedClip.h
diff --git a/src/gpu/GrReducedClip.h b/src/gpu/GrReducedClip.h
index d7b7ea88811c3671389af313b80102142809fff7..fe9e438deadf879618cd291bdb741a79bfd3f482 100644
--- a/src/gpu/GrReducedClip.h
+++ b/src/gpu/GrReducedClip.h
@@ -20,11 +20,6 @@ public:
     GrReducedClip(const SkClipStack& stack, const SkRect& queryBounds);
 
     /**
-     * Uniquely identifies this reduced clip.
-     */
-    int32_t genID() const { return fGenID; }
-
-    /**
      * If hasIBounds() is true, this is the bounding box within which the reduced clip is valid, and
      * the caller must not modify any pixels outside this box. Undefined if hasIBounds() is false.
      */
@@ -48,6 +43,11 @@ public:
     const ElementList& elements() const { return fElements; }
 
     /**
+     * If elements() are nonempty, uniquely identifies the list of elements. Otherwise undefined.

[bsalomon, 2016/08/17 13:34:53]

I don't think it matters other than for the comment, but don't we sometimes
remove elements from the head of the list? That would mean the last element's ID
doesn't uniquely identify the entire list. I believe in practice we use the id
plus the ibounds to uniquely identify.

[csmartdalton, 2016/08/17 14:49:14]

If I follow, then this comment should clear it up?

+     */
+    int32_t elementsGenID() const { SkASSERT(!fElements.isEmpty()); return fElementsGenID; }
+
+    /**
      * Indicates whether antialiasing is required to process any of the clip elements.
      */
     bool requiresAA() const { return fRequiresAA; }
@@ -60,10 +60,10 @@ public:
     InitialState initialState() const { return fInitialState; }
 
 private:
-    int32_t        fGenID;
     SkIRect        fIBounds;
     bool           fHasIBounds;
     ElementList    fElements;
+    int32_t        fElementsGenID;
     bool           fRequiresAA;
     InitialState   fInitialState;
 };