Add Dart example.

3rd-party: include Protolock utility

Add group support for proto2

No changes were needed, but since the Xcode projects pick up the updated
setting, the tests require a newer Xcode that supports Swift 4.

This is being done because Xcode 10 starting warning about Swift 3 support
going away in the future, so we might as well do the updates since most
folks shouldn't be on those really old Xcode versions any more.

Not sure the history for why there were two objc_library targets, but
given the one has an issue about not working, merge them into a single
target and an alias.

- Use the alias for :objectivec since that naming doesn't seem to follow
  the other targets *_library targets here.
- Update :protobuf_objc to be use for the working target and just inline
  the sources/headers lists so there is less indirection in the file.

Fixes #5284

Remove unused types

They're not doing anything, so might as well get rid of them.

Given an argument, the previous implementation was off by one
(`.first(2)` would return 3 elements) compared to the `Enumerable#first`
method.

Fix error: unused parameter 'arena' [-Werror=unused-parameter]

* Remove ruby21 and ruby22 tests

* Update test badge

Add node and php to benchmark dashboard

* Add ruby 2.3, 2.4 and 2.5 test for linux.

* Update kokoro files

* Add back commented gc test

* Fix gc_test failure

* Remove unused code

* Update ruby 2.5.0 to 2.5.1

* Update ruby 2.3 to 2.3.8

* Remove useless comment

Removed unnecessary includes from stubs/common.h

Revert "protobuf_generate(): add relative path to output dir"

Remove unnecessary cast to Builder in generated Java code

Link to libatomic when necessary (eg. on armv6l)

Update third_party.md regarding Erlang

Removing links to Erlang projects which are no longer maintained.

remove obsolete parent

* Replace assert_true/assert_false with assert, because they are not provided in newer version of test/unit

* Use rescue to handle exception subclass

* Commented out the require that caused gc_test failure.

* Commented out test

* Fix typo

* Ported FieldMaskUtil from Java to C#

* Merged FieldMaskUtil into FieldMaskPartial

- Removed FieldMaskUtil
- Moved FieldMaskTree to root
- Updated tests

* Improved tests

- Removed internal method FieldMaskTree.GetFieldPaths
- Proof FieldMask.Paths only contains expected values

* Added FieldMaskTreeTest to Makefile

* Added FieldMaskTree to Makefile

* Add support for primitive types in setters

* Update to address PR feedback

* Add tests and fixes for repeated fields

* Remove repeated field code, add getters

* Cleanup, test getters and oneofs

* Move boxing logic into separate class

* Add tests for wrapper type constructor args

* Update to add new setXXXValue methods

* Fix tests for invalid values

* Fix c extension for wrapper accessors

* Fix the bug that well known types didn't call Message_construct

* Address PR comments

* Refactoring init message with array logic

* Add include path to protoc

* Add missing TSRM_LS defintion

* Fix TSRM_LS

* Fix dist check

* Fix parsing empty Struct Values from Json

This fixes a bug. When parsing a struct from JSON like
    struct = json_format.Parse('{"k": {}}', Struct())
then the struct's "k" value would end up not initialized, and accessing
the value would raise an error.
    In[1]: struct['k']
    ValueError: Value not set
That seems to be because the Struct field of the Value was not set.
    In[2]: struct
    Out[2]:
    fields {
      key: "k"
      value {
      }
    }

This commit makes sure that the Value's Struct field is initialized even
if the Struct has no values itself.

This commit also extends a test to cover this case.

* Additionally test for empty list