Merge remote-tracking branch 'upstream/master' into canonicalize_server_uri

doc/PROTOCOL-WEB.md

gRPC-Core.podspec

gRPC-ProtoRPC.podspec

gRPC-RxLibrary.podspec

gRPC.podspec

src/objective-c/!ProtoCompiler-gRPCPlugin.podspec

src/objective-c/BoringSSL.podspec

src/objective-c/GRPCClient/private/GRPCHost.m

src/objective-c/GRPCClient/private/version.h

src/python/grpcio/commands.py

src/python/grpcio/grpc/__init__.py

src/python/grpcio/grpc/_channel.py

src/python/grpcio/grpc/_common.py

src/python/grpcio/grpc/_plugin_wrapping.py

src/python/grpcio/grpc/_server.py

src/python/grpcio/grpc/_utilities.py

src/python/grpcio/grpc/beta/_client_adaptations.py

src/python/grpcio/grpc/beta/_connectivity_channel.py

src/python/grpcio/grpc/beta/_server_adaptations.py

...python/grpcio/grpc/framework/interfaces/base/utilities.py