third_party/protobuf: Update to HEAD (83d681ee2c)

third_party/protobuf/objectivec/README.md

 Protocol Buffers - Google's data interchange format
 ===================================================
 
 [![Build Status](https://travis-ci.org/google/protobuf.svg?branch=master)](https://travis-ci.org/google/protobuf)
 
 Copyright 2008 Google Inc.
 
 This directory contains the Objective C Protocol Buffers runtime library.
 
 Requirements
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 having an *explicit* and *default* value. You can always get the value of the
 property. In the case that it hasn't been set you will get the default. In
 cases where you need to know whether it was set explicitly or you are just
 getting the default, you can use the `has\[NAME\]` property. If the value has
 been set, and you want to clear it, you can set the `has\[NAME\]` to `NO`.
 *proto3* syntax messages do away with this concept, thus the default values are
 never included when the message is encoded.
 
 The Objective C classes/enums can be used from Swift code.
 
-Objective C Generator Options
------------------------------
+Objective C Generator Proto File Options
+----------------------------------------
 
 **objc_class_prefix=\<prefix\>** (no default)
 
 Since Objective C uses a global namespace for all of its classes, there can
 be collisions. This option provides a prefix that will be added to the Enums
 and Objects (for messages) generated from the proto. Convention is to base
 the prefix on the package the proto is in.
 
+Objective C Generator `protoc` Options
+--------------------------------------
+
+When generating Objective C code, `protoc` supports a `--objc_opt` argument; the
+argument is comma-delimited name/value pairs (_key=value,key2=value2_). The
+_keys_ are used to change the behavior during generation. The currently
+supported keys are:
+
+  * `generate_for_named_framework`: The `value` used for this key will be used
+    when generating the `#import` statements in the generated code.  Instead
+    of being plain `#import "some/path/file.pbobjc.h"` lines, they will be
+    framework based, i.e. - `#import <VALUE/file.pbobjc.h>`.
+
+    _NOTE:_ If this is used with `named_framework_to_proto_path_mappings_path`,
+    then this is effectively the _default_ to use for everything that wasn't
+    mapped by the other.
+
+  * `named_framework_to_proto_path_mappings_path`: The `value` used for this key
+    is a path to a file containing the listing of framework names and proto
+    files. The generator uses this to decide if another proto file referenced
+    should use a framework style import vs. a user level import
+    (`#import <FRAMEWORK/file.pbobjc.h>` vs `#import "dir/file.pbobjc.h"`).
+
+    The format of the file is:
+      * An entry is a line of `frameworkName: file.proto, dir/file2.proto`.
+      * Comments start with `#`.
+      * A comment can go on a line after an entry.
+        (i.e. - `frameworkName: file.proto # comment`)
+
+    Any number of files can be listed for a framework, just separate them with
+    commas.
+
+    There can be multiple lines listing the same frameworkName incase it has a
+    lot of proto files included in it; and having multiple lines makes things
+    easier to read.
+
 Contributing
 ------------
 
 Please make updates to the tests along with changes. If just changing the
 runtime, the Xcode projects can be used to build and run tests. If your change
 also requires changes to the generated code,
 `objectivec/DevTools/full_mac_build.sh` can be used to easily rebuild and test
 changes. Passing `-h` to the script will show the addition options that could
 be useful.
 
 Documentation
 -------------
 
 The complete documentation for Protocol Buffers is available via the
 web at:
 
     https://developers.google.com/protocol-buffers/