simplify code in SkRecords.h

src/core/SkRecordPattern.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkRecordPattern_DEFINED
 #define SkRecordPattern_DEFINED
 
@@ skipping 23 matching lines @@
         fPtr = nullptr;
         return false;
     }
 
 private:
     type* fPtr;
 };
 
 // Matches any command that draws, and stores its paint.
 class IsDraw {
-    SK_CREATE_MEMBER_DETECTOR(paint);
 public:
     IsDraw() : fPaint(nullptr) {}
 
     typedef SkPaint type;
     type* get() { return fPaint; }
 
     template <typename T>
-    SK_WHEN(HasMember_paint<T>, bool) operator()(T* draw) {
+    SK_WHEN(T::kTags & kDraw_Tag, bool) operator()(T* draw) {
         fPaint = AsPtr(draw->paint);
         return true;
     }
 
+    bool operator()(DrawDrawable*) {
+        static_assert(DrawDrawable::kTags & kDraw_Tag, "");
+        fPaint = nullptr;
+        return true;
+    }
+
     template <typename T>
-    SK_WHEN(!HasMember_paint<T>, bool) operator()(T*) {
+    SK_WHEN(!(T::kTags & kDraw_Tag), bool) operator()(T* draw) {
         fPaint = nullptr;
         return false;
     }
-
-    // SaveLayer has an SkPaint named paint, but it's not a draw.
-    bool operator()(SaveLayer*) {
-        fPaint = nullptr;
-        return false;
-    }
 
 private:
     // Abstracts away whether the paint is always part of the command or optional.
     template <typename T> static T* AsPtr(SkRecords::Optional<T>& x) { return x; }
     template <typename T> static T* AsPtr(T& x) { return &x; }
 
     type* fPaint;
 };
 
 // Matches if Matcher doesn't.  Stores nothing.
@@ skipping 120 matching lines @@
 
 template <typename A, typename B, typename C, typename D, typename E, typename F>
 struct Pattern6 : Cons<A, Pattern5<B, C, D, E, F> > {};
 
 template <typename A, typename B, typename C, typename D, typename E, typename F, typename G>
 struct Pattern7 : Cons<A, Pattern6<B, C, D, E, F, G> > {};
 
 }  // namespace SkRecords
 
 #endif//SkRecordPattern_DEFINED