Important Changes:

Features:

Provide demos for manual flow-control and back-pressure
Beginning of support for full-stream compression (as an alternative to per-message compression). Currently only client-side decompression is implemented. This work is experimental
io.grpc.Context now emits a SEVERE warning if it detects the length is abnormally long
Record individual message sizes with Census/Tracing
Allow to fallback to ServiceLoader.load without Classloader to make gRPC more OSGi friendly
Minor memory reductions
ManagedChannels log a warning when not properly shutdown

Fix GET support in OkHttp client to actually use HTTP GET. This is still considered experimental.
Fix Bazel naming mixup with gson and opencensus. This only matters if you were passing omit_com_google_code_gson=True or omit_io_opencensus_api=True to grpc_java_repositories() (#3379)
Fix Bazel java_grpc_library() rule when depending on protos in external repos (#3483)
Fix transport improperly notifying Channel of its use in certain cases. This could cause spurious disconnections when idleTimeout() is configured on the Channel (#3374)
We now wait until all streams are closed before gracefully terminating a Netty connection. There was previously a five second timeout (#3386)

Metadata entries for reserved headers are stripped (“user-agent”, “content-type”, “te”)
InprocessChannelBuilder and InprocessServerBuilder now throw an exception when using the static constructor inherited from their base class. These didn't do what users expected, as they were actually just calling the ManagedChannelBuilder/ServerBuilder methods.