Add asRRect method to SkClipStack::Element

include/core/SkClipStack.h

Index: include/core/SkClipStack.h
diff --git a/include/core/SkClipStack.h b/include/core/SkClipStack.h
index 38d6d6751d7506aad3b797bcd6a121b752459003..e4f2563adea072ee523da8cd80ec5c3ce7df1e57 100644
--- a/include/core/SkClipStack.h
+++ b/include/core/SkClipStack.h
@@ -98,6 +98,19 @@ public:
         //!< Call to get the element as a path, regardless of its type.
         void asPath(SkPath* path) const;
 
+        //!< Call to get the element as a round rect. Returns nullptr if this is not satisfiable.
+        const SkRRect* asRRect() const {

[bsalomon, 2016/03/16 13:17:11]

Maybe we should just loosen the restrictions on when getRRect() can be called?
This shares the "as" Name with "asPath". However, that method always succeeds,
whereas this one does not.

[Chris Dalton, 2016/03/16 15:17:56]

Right, I gave it the "as" name because they both have the property of
generalizing specialized types to a more general type of shape.

The problem with loosening the restrictions on getRRect() is that it seems we
would then have to loosen the restrictions on getPath() as well, just out if
principle.

What if we keep the "as" name, but assert it's not a path instead of returning
null when we can't generalize it? Then it's the caller's responsibility to check
it isn't a path before calling.

+            switch (fType) {
+                case kRect_Type:
+                    SkASSERT(SkRRect::kRect_Type == fRRect.getType());
+                    // fallthrough
+                case kRRect_Type:
+                    return &fRRect;
+                default:
+                    return nullptr;
+            }
+        }
+
         /** If getType() is not kEmpty this indicates whether the clip shape should be anti-aliased
             when it is rasterized. */
         bool isAA() const { return fDoAA; }