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

third_party/protobuf/objectivec/GPBMessage_PackagePrivate.h

 // Protocol Buffers - Google's data interchange format
 // Copyright 2008 Google Inc.  All rights reserved.
 // https://developers.google.com/protocol-buffers/
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 // notice, this list of conditions and the following disclaimer.
@@ skipping 49 matching lines @@
 
   // A lock to provide mutual exclusion from internal data that can be modified
   // by *read* operations such as getters (autocreation of message fields and
   // message extensions, not setting of values). Used to guarantee thread safety
   // for concurrent reads on the message.
   // NOTE: OSSpinLock may seem like a good fit here but Apple engineers have
   // pointed out that they are vulnerable to live locking on iOS in cases of
   // priority inversion:
   //   http://mjtsai.com/blog/2015/12/16/osspinlock-is-unsafe/
   //   https://lists.swift.org/pipermail/swift-dev/Week-of-Mon-20151214/000372.html
+  // Use of readOnlySemaphore_ must be prefaced by a call to
+  // GPBPrepareReadOnlySemaphore to ensure it has been created. This allows
+  // readOnlySemaphore_ to be only created when actually needed.
+  dispatch_once_t readOnlySemaphoreCreationOnce_;
   dispatch_semaphore_t readOnlySemaphore_;
 }
 
 // Gets an extension value without autocreating the result if not found. (i.e.
 // returns nil if the extension is not set)
 - (id)getExistingExtension:(GPBExtensionDescriptor *)extension;
 
 // Returns an array of GPBExtensionDescriptor* for all the extensions currently
 // in use on the message.  They are sorted by field number.
 - (NSArray *)sortedExtensionsInUse;
@@ skipping 16 matching lines @@
 - (void)mergeDelimitedFromCodedInputStream:(GPBCodedInputStream *)input
                          extensionRegistry:
                              (GPBExtensionRegistry *)extensionRegistry;
 
 - (void)addUnknownMapEntry:(int32_t)fieldNum value:(NSData *)data;
 
 @end
 
 CF_EXTERN_C_BEGIN
 
+
+// Call this before using the readOnlySemaphore_. This ensures it is created only once.
+NS_INLINE void GPBPrepareReadOnlySemaphore(GPBMessage *self) {
+  dispatch_once(&self->readOnlySemaphoreCreationOnce_, ^{
+    self->readOnlySemaphore_ = dispatch_semaphore_create(1);
+  });
+}
+
 // Returns a new instance that was automatically created by |autocreator| for
 // its field |field|.
 GPBMessage *GPBCreateMessageWithAutocreator(Class msgClass,
                                             GPBMessage *autocreator,
                                             GPBFieldDescriptor *field)
     __attribute__((ns_returns_retained));
 
 // Returns whether |message| autocreated this message. This is NO if the message
 // was not autocreated by |message| or if it has been mutated since
 // autocreation.
 BOOL GPBWasMessageAutocreatedBy(GPBMessage *message, GPBMessage *parent);
 
 // Call this when you mutate a message. It will cause the message to become
 // visible to its autocreator.
 void GPBBecomeVisibleToAutocreator(GPBMessage *self);
 
 // Call this when an array/dictionary is mutated so the parent message that
 // autocreated it can react.
 void GPBAutocreatedArrayModified(GPBMessage *self, id array);
 void GPBAutocreatedDictionaryModified(GPBMessage *self, id dictionary);
 
 // Clear the autocreator, if any. Asserts if the autocreator still has an
 // autocreated reference to this message.
 void GPBClearMessageAutocreator(GPBMessage *self);
 
 CF_EXTERN_C_END