Fix SkTFits in to work properly with signed/unsigned mixtures.

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.
+ */
+
+#ifndef SkTLogic_DEFINED
+#define SkTLogic_DEFINED
+
+/** SkTBool::type = self; SkTBool::value = b; */
+template <bool b> struct SkTBool {
+    typedef SkTBool type;
+    static const bool value = b;
+};
+typedef SkTBool<true> SkTrue;
+typedef SkTBool<false> SkFalse;
+
+/** SkTIf_c::type = (condition) ? T : F; */
+template <bool condition, typename T, typename F> struct SkTIf_c {
+    typedef F type;
+};
+template <typename T, typename F> struct SkTIf_c<true, T, F> {
+    typedef T type;
+};
+
+/** SkTIf::type = (Condition::value) ? T : F; */
+template <typename Condition, typename T, typename F> struct SkTIf {
+    typedef typename SkTIf_c<static_cast<bool>(Condition::value), T, F>::type type;
+};
+
+/** SkTMux::type = (a && b) ? Both : (a) ? A : (b) ? B : Neither; */
+template <typename a, typename b, typename Both, typename A, typename B, typename Neither>
+struct SkTMux {
+    typedef typename SkTIf<a, typename SkTIf<b, Both, A>::type,
+                              typename SkTIf<b, B, Neither>::type>::type type;
+};
+
+/** SkTEnableIf_c::type = (condition) ? T : [does not exist]; */
+template <bool condition, class T = void> struct SkTEnableIf_c { };
+template <class T> struct SkTEnableIf_c<true, T> {
+    typedef T type;
+};
+
+/** SkTEnableIf::type = (Condition::value) ? T : [does not exist]; */
+template <class Condition, class T = void> struct SkTEnableIf
+    : public SkTEnableIf_c<static_cast<bool>(Condition::value), T> { };
+
+#endif