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

doc/images/load_balancing_design.png

doc/load-balancing.md

gRPC-Core.podspec

src/core/ext/client_config/channel_connectivity.c

...e-c/tests/CoreCronetEnd2EndTests/CoreCronetEnd2EndTests.m

src/objective-c/tests/CoreCronetEnd2EndTests/Info.plist

src/objective-c/tests/Podfile

src/objective-c/tests/Tests.xcodeproj/project.pbxproj

...oj/xcshareddata/xcschemes/CoreCronetEnd2EndTests.xcscheme

src/php/ext/grpc/call.c

src/php/ext/grpc/call.h

src/php/ext/grpc/call_credentials.c

src/php/ext/grpc/call_credentials.h

src/php/ext/grpc/channel.c

src/php/ext/grpc/channel.h

src/php/ext/grpc/channel_credentials.c

src/php/ext/grpc/channel_credentials.h

src/php/ext/grpc/php_grpc.c

src/php/ext/grpc/php_grpc.h

src/php/ext/grpc/server.c