Add SkMSAN.h

src/core/SkMSAN.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 SkMSAN_DEFINED
+#define SkMSAN_DEFINED
+
+#include <stddef.h>  // size_t
+
+// Typically declared in LLVM's msan_interface.h.  Easier for us to just re-declare.
+extern "C" {
+    void __msan_check_mem_is_initialized(const volatile void*, size_t);
+}
+
+// Code that requires initialized inputs can call this to make it clear that
+// the blame for use of uninitialized data belongs further up the call stack.
+static inline void sk_msan_assert_initialized(const void* begin, const void* end) {
+#if defined(__has_feature)
+    #if __has_feature(memory_sanitizer)
+        __msan_check_mem_is_initialized(begin, (const char*)end - (const char*)begin);
+    #endif
+#endif
+}
+
+#endif//SkMSAN_DEFINED