Simplify mask/clip intersection, making sure to explicitly check for an empty mask.

src/core/SkDraw.cpp

Index: src/core/SkDraw.cpp
diff --git a/src/core/SkDraw.cpp b/src/core/SkDraw.cpp
index 24fc9064a6dd092a91301d3608834fb9256f9b87..f615b83d1678f2fd9bae249df34e4ecbd4264ced 100644
--- a/src/core/SkDraw.cpp
+++ b/src/core/SkDraw.cpp
@@ -1488,19 +1488,14 @@ public:
                 } while (!clipper.done());
             }
         } else {
-            SkIRect  storage;
-            SkIRect* bounds = &mask.fBounds;
-
-            // this extra test is worth it, assuming that most of the time it succeeds
-            // since we can avoid writing to storage
-            if (!fClipBounds.containsNoEmptyCheck(mask.fBounds)) {
-                if (!storage.intersectNoEmptyCheck(mask.fBounds, fClipBounds))
-                    return;
-                bounds = &storage;
+            SkIRect storage;
+            if (mask.fBounds.isEmpty() ||

[reed1, 2016/06/17 10:39:42]

I wonder 

1. if it would be clearer to put this empty check after line 1478, since we care
about empty/inverted in both cases.
2. we add a comment explaining why we need to check, even though the logic on
lines 1474-5 would seem to mean we could never be empty/inverted.

+                    !storage.intersectNoEmptyCheck(mask.fBounds, fClipBounds)) {
+                return;
             }
 
             if (this->getImageData(glyph, &mask)) {
-                this->blitMask(mask, *bounds);
+                this->blitMask(mask, storage);
             }
         }
     }