Update //third_party/protobuf to version 3.

third_party/protobuf/CONTRIBUTORS.txt

Index: third_party/protobuf/CONTRIBUTORS.txt
diff --git a/third_party/protobuf/CONTRIBUTORS.txt b/third_party/protobuf/CONTRIBUTORS.txt
index dda3b3597b8119a03e36f5cab8f03d6c836ead13..b8d97fc23d85b145367eabf6249cd4aed755bb32 100644
--- a/third_party/protobuf/CONTRIBUTORS.txt
+++ b/third_party/protobuf/CONTRIBUTORS.txt
@@ -17,6 +17,12 @@ Proto2 Python primary authors:
   Will Robinson <robinson@google.com>
   Petar Petrov <petar@google.com>
 
+Java Nano primary authors:
+  Brian Duff <bduff@google.com>
+  Tom Chao <chaot@google.com>
+  Max Cai <maxtroy@google.com>
+  Ulas Kirazci <ulas@google.com>
+
 Large code contributions:
   Jason Hsueh <jasonh@google.com>
   Joseph Schorr <jschorr@google.com>
@@ -86,3 +92,11 @@ Patch contributors:
     * Fix bug with permanent callbacks that delete themselves when run.
   Michael Kucharski <m.kucharski@gmail.com>
     * Added CodedInputStream.getTotalBytesRead().
+  Kacper Kowalik <xarthisius.kk@gmail.com>
+    * Fixed m4/acx_pthread.m4 problem for some Linux distributions.
+  William Orr <will@worrbase.com>
+    * Fixed detection of sched_yield on Solaris.
+    * Added atomicops for Solaris
+  Andrew Paprocki <andrew@ishiboo.com>
+    * Fixed minor IBM xlC compiler build issues
+    * Added atomicops for AIX (POWER)