Annotate ThreadData::PushToHeadOfList for MemorySanitizer.

base/compiler_specific.h

Index: base/compiler_specific.h
diff --git a/base/compiler_specific.h b/base/compiler_specific.h
index 5d7d9d11019bd22bc0a9c9e28f06ccb036566a5e..01c1eb1939b52cc0493f0d8af8b38da15aca33fa 100644
--- a/base/compiler_specific.h
+++ b/base/compiler_specific.h
@@ -166,4 +166,19 @@
 // If available, it would look like:
 //   __attribute__((format(wprintf, format_param, dots_param)))
 
+
+// MemorySanitizer annotations.
+#ifdef MEMORY_SANITIZER
+extern "C" {
+void __msan_unpoison(const void *p, unsigned long s);
+}  // extern "C"
+
+// Mark a memory region fully initialized.
+// Use this to annotate code that deliberately reads uninitialized data, for
+// example a GC scavenging root set pointers from the stack.
+#define MSAN_UNPOISON(p, s)  __msan_unpoison(p, s)
+#else  // MEMORY_SANITIZER
+#define MSAN_UNPOISON(p, s)
+#endif  // MEMORY_SANITIZER
+
 #endif  // BASE_COMPILER_SPECIFIC_H_