Add comparison and assignment to SkClipStack (and fix an optimization bug).

Review URL: http://codereview.appspot.com/4423085

git-svn-id: http://skia.googlecode.com/svn/trunk@1230 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/include/core/SkClipStack.h b/include/core/SkClipStack.h
index 850a3f0..b94ae19 100644
--- a/include/core/SkClipStack.h
+++ b/include/core/SkClipStack.h
@@ -10,8 +10,13 @@
 class SK_API SkClipStack {
 public:
     SkClipStack();
+    SkClipStack(const SkClipStack& b);
     ~SkClipStack() {}
 
+    SkClipStack& operator=(const SkClipStack& b);
+    bool operator==(const SkClipStack& b) const;
+    bool operator!=(const SkClipStack& b) const { return !(*this == b); }
+
     void reset();
 
     int getSaveCount() const { return fSaveCount; }