Merge branch 'master' into add_proto

Makefile

src/core/ext/transport/cronet/transport/cronet_transport.c

src/core/lib/iomgr/tcp_server_posix.c

src/csharp/Grpc.Core.Tests/ClientServerTest.cs

src/csharp/Grpc.Core.Tests/ContextPropagationTest.cs

src/csharp/Grpc.Core.Tests/GrpcEnvironmentTest.cs

src/csharp/Grpc.Core.Tests/Internal/AsyncCallServerTest.cs

src/csharp/Grpc.Core.Tests/Internal/AsyncCallTest.cs

src/csharp/Grpc.Core.Tests/MarshallingErrorsTest.cs

src/csharp/Grpc.Core/Channel.cs

src/csharp/Grpc.Core/Grpc.Core.csproj

src/csharp/Grpc.Core/GrpcEnvironment.cs

src/csharp/Grpc.Core/Internal/AsyncCall.cs

src/csharp/Grpc.Core/Internal/AsyncCallBase.cs

src/csharp/Grpc.Core/Internal/AsyncCallServer.cs

src/csharp/Grpc.Core/Internal/AsyncCompletion.cs

src/csharp/Grpc.Core/Internal/CallSafeHandle.cs

src/csharp/Grpc.Core/Internal/ChannelSafeHandle.cs

src/csharp/Grpc.Core/Internal/ClientRequestStream.cs

src/csharp/Grpc.Core/Internal/CompletionQueueSafeHandle.cs