Add isScale2d() helper function to SkMatrix44.

include/utils/SkMatrix44.h

Index: include/utils/SkMatrix44.h
diff --git a/include/utils/SkMatrix44.h b/include/utils/SkMatrix44.h
index 553e8d7c4f9d0551e73f4bf97368b6d29e6b2d83..90f29a994a77eeb480500c6e1345ae1a76e7aeaf 100644
--- a/include/utils/SkMatrix44.h
+++ b/include/utils/SkMatrix44.h
@@ -225,6 +225,13 @@ public:
         return !(this->getType() & ~(kScale_Mask | kTranslate_Mask));
     }
 
+    /**
+     *  Returns true if the matrix only contains scale or is identity.
+     */
+    inline bool isScale() const {
+            return !(this->getType() & ~kScale_Mask);
+    }
+
     inline bool hasPerspective() const {
         return SkToBool(this->getType() & kPerspective_Mask);
     }