Implement missing context methods (#363)

Author: ocelotl

CHANGELOG.md

@@ -22,6 +22,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [0.19b0](https://github.com/open-telemetry/opentelemetry-python-contrib/releases/tag/v0.19b0) - 2021-03-26
 
+- Implement context methods for `_InterceptorChannel`
+  ([#363](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/363))
+
 ### Changed
 - Rename `IdsGenerator` to `IdGenerator`
   ([#350](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/350))

instrumentation/opentelemetry-instrumentation-grpc/src/opentelemetry/instrumentation/grpc/grpcext/_interceptor.py

@@ -232,11 +232,11 @@ def close(self):
 
     def __enter__(self):
         """Enters the runtime context related to the channel object."""
-        raise NotImplementedError()
+        return self
 
     def __exit__(self, exc_type, exc_val, exc_tb):
         """Exits the runtime context related to the channel object."""
-        raise NotImplementedError()
+        self.close()
 
 
 def intercept_channel(channel, *interceptors):