Update //third_party/protobuf to version 3.

third_party/protobuf/patches/0002-remove-support-for-unnecessary-languages.patch

+--- protobuf-cleaned/src/google/protobuf/compiler/main.cc       2015-12-30 13:21:46.000000000 -0800
++++ protobuf-patched/src/google/protobuf/compiler/main.cc       2016-03-31 13:25:41.548005626 -0700
+@@ -33,12 +33,6 @@
+ #include <google/protobuf/compiler/command_line_interface.h>
+ #include <google/protobuf/compiler/cpp/cpp_generator.h>
+ #include <google/protobuf/compiler/python/python_generator.h>
+-#include <google/protobuf/compiler/java/java_generator.h>
+-#include <google/protobuf/compiler/javanano/javanano_generator.h>
+-#include <google/protobuf/compiler/ruby/ruby_generator.h>
+-#include <google/protobuf/compiler/csharp/csharp_generator.h>
+-#include <google/protobuf/compiler/objectivec/objectivec_generator.h>
+-#include <google/protobuf/compiler/js/js_generator.h>
+ 
+ int main(int argc, char* argv[]) {
+ 
+@@ -50,41 +44,10 @@
+   cli.RegisterGenerator("--cpp_out", "--cpp_opt", &cpp_generator,
+                         "Generate C++ header and source.");
+ 
+-  // Proto2 Java

[Peter Kasting, 2016/04/15 01:12:59]

I wonder if the Android people might actually want this?  Similarly the ObjC
generator for the iOS folks.

Now that all these files are in our tree, do we really gain much by stripping
out these languages?  Seems like it'd be easier to just drop this patch, and
include the full filelists in the buildfiles.  That'd make the buildfiles look
more like copies of the filelists in the upstream buildfiles anyway.

[xyzzyz, 2016/04/15 20:50:36]

Android/iOS doesn't seem to be using it. 

The drawback of this is that it increases the build time by adding dozens of
additional targets. I don't know if this is significant, though. To keep our
changes to upstream minimal, I added these back.

+-  google::protobuf::compiler::java::JavaGenerator java_generator;
+-  cli.RegisterGenerator("--java_out", &java_generator,
+-                        "Generate Java source file.");
+-
+-
+   // Proto2 Python
+   google::protobuf::compiler::python::Generator py_generator;
+   cli.RegisterGenerator("--python_out", &py_generator,
+                         "Generate Python source file.");
+ 
+-  // Java Nano
+-  google::protobuf::compiler::javanano::JavaNanoGenerator javanano_generator;
+-  cli.RegisterGenerator("--javanano_out", &javanano_generator,
+-                        "Generate Java Nano source file.");
+-
+-  // Ruby
+-  google::protobuf::compiler::ruby::Generator rb_generator;
+-  cli.RegisterGenerator("--ruby_out", &rb_generator,
+-                        "Generate Ruby source file.");
+-
+-  // CSharp
+-  google::protobuf::compiler::csharp::Generator csharp_generator;
+-  cli.RegisterGenerator("--csharp_out", "--csharp_opt", &csharp_generator,
+-                        "Generate C# source file.");
+-
+-  // Objective C
+-  google::protobuf::compiler::objectivec::ObjectiveCGenerator objc_generator;
+-  cli.RegisterGenerator("--objc_out", &objc_generator,
+-                        "Generate Objective C header and source.");
+-
+-  // JavaScript
+-  google::protobuf::compiler::js::Generator js_generator;
+-  cli.RegisterGenerator("--js_out", &js_generator,
+-                        "Generate JavaScript source.");
+-
+   return cli.Run(argc, argv);
+ }