Annotate V8 for MemorySanitizer.

src/frames.cc

Index: src/frames.cc
===================================================================
--- src/frames.cc	(revision 17104)
+++ src/frames.cc	(working copy)
@@ -33,6 +33,7 @@
 #include "full-codegen.h"
 #include "lazy-instance.h"
 #include "mark-compact.h"
+#include "msan.h"
 #include "safepoint-table.h"
 #include "scopeinfo.h"
 #include "string-stream.h"
@@ -424,6 +425,7 @@
     holder = reinterpret_cast<Code*>(code);
     pc = holder->instruction_start() + pc_offset;
     *pc_address = pc;
+    MSAN_MEMORY_IS_INITIALIZED(pc_address, sizeof(*pc_address));
   }
 }