Merge github.com:grpc/grpc into no-worries-i-can-wait

.gitignore

doc/connection-backoff.md

include/grpc++/impl/call.h

include/grpc/support/port_platform.h

src/compiler/objective_c_generator.cc

src/core/iomgr/socket_windows.c

src/core/iomgr/tcp_server_windows.c

src/core/transport/chttp2/frame_data.c

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

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

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

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

src/csharp/Grpc.Core/Calls.cs

src/csharp/Grpc.Core/Channel.cs

src/csharp/Grpc.Core/GrpcEnvironment.cs

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

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

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

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

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