Update third_party/protobuf to protobuf-v3.0.0-beta-3

third_party/protobuf/src/google/protobuf/generated_message_reflection.h

Index: third_party/protobuf/src/google/protobuf/generated_message_reflection.h
diff --git a/third_party/protobuf/src/google/protobuf/generated_message_reflection.h b/third_party/protobuf/src/google/protobuf/generated_message_reflection.h
index b26bbbc891cbf0eb98ebb1506f489459a40d3d1a..15fc802ce18eafaad362a7a5aaf3837f3d809064 100644
--- a/third_party/protobuf/src/google/protobuf/generated_message_reflection.h
+++ b/third_party/protobuf/src/google/protobuf/generated_message_reflection.h
@@ -582,11 +582,6 @@ class LIBPROTOBUF_EXPORT GeneratedMessageReflection : public Reflection {
 // which the offsets of the direct fields of a class are non-constant.
 // Fields inherited from superclasses *can* have non-constant offsets,
 // but that's not what this macro will be used for.
-//
-// Note that we calculate relative to the pointer value 16 here since if we
-// just use zero, GCC complains about dereferencing a NULL pointer.  We
-// choose 16 rather than some other number just in case the compiler would
-// be confused by an unaligned pointer.
 #if defined(__clang__)
 // For Clang we use __builtin_offsetof() and suppress the warning,
 // to avoid Control Flow Integrity and UBSan vptr sanitizers from
@@ -597,6 +592,10 @@ class LIBPROTOBUF_EXPORT GeneratedMessageReflection : public Reflection {
   __builtin_offsetof(TYPE, FIELD)                             \
   _Pragma("clang diagnostic pop")
 #else
+// Note that we calculate relative to the pointer value 16 here since if we
+// just use zero, GCC complains about dereferencing a NULL pointer.  We
+// choose 16 rather than some other number just in case the compiler would
+// be confused by an unaligned pointer.
 #define GOOGLE_PROTOBUF_GENERATED_MESSAGE_FIELD_OFFSET(TYPE, FIELD)    \
   static_cast<int>(                                           \
       reinterpret_cast<const char*>(                          \