MethodDescriptor.setRawMethodName breaks Immutability if multiple types of transport are used

[dapengzhang0]

java.lang.ClassCastException: io.netty.util.AsciiString cannot be cast to io.grpc.netty.shaded.io.netty.util.AsciiString
	at io.grpc.netty.shaded.io.grpc.netty.NettyClientStream$Sink.writeHeadersInternal(NettyClientStream.java:130)
	at io.grpc.netty.shaded.io.grpc.netty.NettyClientStream$Sink.writeHeaders(NettyClientStream.java:122)
	at io.grpc.internal.AbstractClientStream.start(AbstractClientStream.java:166)
	at io.grpc.internal.ForwardingClientStream.start(ForwardingClientStream.java:87)
	at io.grpc.internal.InternalSubchannel$CallTracingTransport$1.start(InternalSubchannel.java:645)
	at io.grpc.internal.DelayedStream$5.run(DelayedStream.java:229)
	at io.grpc.internal.DelayedStream.drainPendingCalls(DelayedStream.java:163)
	at io.grpc.internal.DelayedStream.setStream(DelayedStream.java:132)
	at io.grpc.internal.DelayedClientTransport$PendingStream.createRealStream(DelayedClientTransport.java:358)
	at io.grpc.internal.DelayedClientTransport$PendingStream.access$300(DelayedClientTransport.java:341)
	at io.grpc.internal.DelayedClientTransport$5.run(DelayedClientTransport.java:300)
	at io.grpc.stub.ClientCalls$ThreadlessExecutor.waitAndDrain(ClientCalls.java:691)
	at io.grpc.stub.ClientCalls.blockingUnaryCall(ClientCalls.java:133)
	at io.grpc.testing.integration.TestServiceGrpc$TestServiceBlockingStub.unaryCall(TestServiceGrpc.java:637)
	at io.grpc.testing.integration.CompressionTest.compression(CompressionTest.java:202)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.junit.internal.runners.statements.FailOnTimeout$CallableStatement.call(FailOnTimeout.java:298)
	at org.junit.internal.runners.statements.FailOnTimeout$CallableStatement.call(FailOnTimeout.java:292)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.lang.Thread.run(Thread.java:748)

[ejona86]

We should probably have InternalMethodDescriptor (atomically) allocate an id when it is constructed. We would extend MethodDescriptor.rawMethodNames to be of size 3 or 4. If the id is above 3/4, then get() would always return null and set() would do nothing.