SkPDF: SkPDFFont class changes

include/private/SkBitmaskEnum.h

+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+#ifndef SkEnumOperators_DEFINED
+#define SkEnumOperators_DEFINED
+
+#include "SkTLogic.h"
+
+namespace skstd {
+template <typename T> struct is_bitmask_enum : std::false_type {};
+}
+
+template <typename E> SK_WHEN(skstd::is_bitmask_enum<E>::value, E) operator|(E l, E r) {
+    using U = skstd::underlying_type_t<E>;
+    return static_cast<E>(static_cast<U>(l) | static_cast<U>(r));
+}
+
+template <typename E> SK_WHEN(skstd::is_bitmask_enum<E>::value, E&) operator|=(E& l, E r) {
+    return l = l | r;
+}
+
+template <typename E> SK_WHEN(skstd::is_bitmask_enum<E>::value, E) operator&(E l, E r) {
+    using U = skstd::underlying_type_t<E>;
+    return static_cast<E>(static_cast<U>(l) & static_cast<U>(r));
+}
+
+template <typename E> SK_WHEN(skstd::is_bitmask_enum<E>::value, E&) operator&=(E& l, E r) {
+    return l = l & r;
+}
+
+#endif  // SkEnumOperators_DEFINED