core,stub: Add toString() to ClientCallImpl and GrpcFuture

[groakley]

Improves debugging experience with ClientCall instances.

Sent on behalf of @charlesmunger

[groakley]

Hmm, looks like this project is being built against Guava version 20.0. pendingToString() was added in 23.0. Are there any plans to bump the Guava version?

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[groakley]

Updated corp CLA status.

[ejona86]

@groakley, it seems the CLA is still a bit unhappy with you. I think #3961 is a blocker for us going as far as Guava 23. It'll happen, but take a little bit. pendingToString() is just an overridden method, not something you call, so it should be fine to have the method and just not put an @Override. If a user is using a newer Guava, they'll get the better toString.

[charlesmunger]

@ejona86 #3961 shouldn't be a blocker for adopting newer versions of guava, since guava has two versions - one for java 8, one for android.

https://github.com/google/guava/wiki/Release22#new-android-version

Does grpc publish separate targets for android and not-android?

[ejona86]

@charlesmunger, the Android version of Guava uses JDK 7 bytecode. The number of Java 6 users should be low, but it is a prerequisite.

[dapengzhang0]

We are using Guava MoreObjects.ToStringHelper instead of harding coding =[]

Ditto.

[groakley]

Commenting again with hopes that I've jumped through the CLA hoops properly.

[dapengzhang0]

LGTM

[ejona86]

Thank you!