Whitelist serialized objects wrt MSAN.

R=jochen@chromium.org
BUG=chromium:457459
LOG=N

Review URL: https://codereview.chromium.org/919613002

Cr-Commit-Position: refs/heads/master@{#26578}

src/serialize.cc

@@ -2120,6 +2120,10 @@ int Serializer::ObjectSerializer::OutputRawData(
     }
 
     const char* description = code_object_ ? "Code" : "Byte";
+#ifdef MEMORY_SANITIZER
+    // Object sizes are usually rounded up with uninitialized padding space.
+    MSAN_MEMORY_IS_INITIALIZED(object_start + base, bytes_to_output);
+#endif  // MEMORY_SANITIZER
     sink_->PutRaw(object_start + base, bytes_to_output, description);
     if (code_object_) delete[] object_start;
   }