Add pattern matchers for SkRecord

src/utils/SkTLogic.h

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  *
  *
  * This header provides some of the helpers (std::integral_constant) and
  * type transformations (std::conditional) which will become available with
  * C++11 in the type_traits header.
@@ skipping 71 matching lines @@
     struct Fallback { int member; };                                                \
     struct Derived : T, Fallback {};                                                \
     template <typename U, U> struct Check;                                          \
     template <typename U> static uint8_t func(Check<int Fallback::*, &U::member>*); \
     template <typename U> static uint16_t func(...);                                \
 public:                                                                             \
     typedef HasMember_##member type;                                                \
     static const bool value = sizeof(func<Derived>(NULL)) == sizeof(uint16_t);      \
 }
 
+// Same sort of thing as SK_CREATE_MEMBER_DETECTOR, but checks for the existence of a nested type.
+#define SK_CREATE_TYPE_DETECTOR(type)                                   \
+template <typename T>                                                   \
+class HasType_##type {                                                  \
+    template <typename U> static uint8_t func(typename U::type*);       \
+    template <typename U> static uint16_t func(...);                    \
+public:                                                                 \
+    static const bool value = sizeof(func<T>(NULL)) == sizeof(uint8_t); \
+}
+
 #endif