Add CallbackConstructorRegistry and semantics of ModelConfigFig.verbose

[caisq]

• Add tfl.CallbackConstructorRegistry. Later the registry will be used in tfjs-node to register the ProgbarLogger.
• Implement semantics of ModelFitConfig.verbose.

Towards: tensorflow/tfjs#631

This change is 

[nsthorat]

Reviewed 5 of 5 files at r1.
Reviewable status: 0 of 1 approvals obtained (waiting on @caisq, @nsthorat, @davidsoergel, and @nkreeger)

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src/base_callbacks.ts, line 610 at r1 (raw file):

      constructors.forEach(ctor => {
        if (ctor === callbackConstructor) {
          throw new ValueError('Duplicate callback constructor.');

print the name?

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src/base_callbacks_test.ts, line 249 at r1 (raw file):

  beforeEach(() => {
    // tslint:disable-next-line:no-any
    (CallbackConstructorRegistry as any).clear();

do you need this cast?

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src/base_callbacks_test.ts, line 331 at r1 (raw file):

  beforeEach(() => {
    // tslint:disable-next-line:no-any
    (CallbackConstructorRegistry as any).clear();

do you need this cast?

[caisq]

Thanks for the review!

Reviewable status: complete! 1 of 1 approvals obtained (waiting on @caisq, @davidsoergel, and @nkreeger)

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src/base_callbacks.ts, line 610 at r1 (raw file):

Previously, nsthorat (Nikhil Thorat) wrote…

print the name?

There is no reliably usable name for the constructor, as it may get minimized.

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src/base_callbacks_test.ts, line 249 at r1 (raw file):

Previously, nsthorat (Nikhil Thorat) wrote…

do you need this cast?

Yes. The clear method is a protected method. I don't want to make it public because there is no need for the user to clear the registered callbacks. It is only for testing.

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src/base_callbacks_test.ts, line 331 at r1 (raw file):

Previously, nsthorat (Nikhil Thorat) wrote…

do you need this cast?

Same as above.