[core] Dispose all webgl programs when disposing the backend.

[dsmilkov]

This change is 

[nsthorat]

Reviewable status: complete! 1 of 1 approvals obtained (waiting on @dsmilkov, @nsthorat, and @pyu10055)

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tfjs-core/src/backends/webgl/backend_webgl.ts, line 2632 at r1 (raw file):

      return;
    }
    if (!ENV.getBool('IS_TEST')) {

use env(), ENV is going to go away

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tfjs-core/src/backends/webgl/backend_webgl_test.ts, line 240 at r1 (raw file):

    tf.backend().dispose();

    // Make sure the cache is empty.

instead of this how about just making a new MathBackendWebGL() and making sure new things can be run (rather than checking these implementation details)?

[dsmilkov]

Reviewable status: complete! 1 of 1 approvals obtained (waiting on @pyu10055)

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tfjs-core/src/backends/webgl/backend_webgl.ts, line 2632 at r1 (raw file):

Previously, nsthorat (Nikhil Thorat) wrote…

use env(), ENV is going to go away

Done.

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tfjs-core/src/backends/webgl/backend_webgl_test.ts, line 240 at r1 (raw file):

Previously, nsthorat (Nikhil Thorat) wrote…

instead of this how about just making a new MathBackendWebGL() and making sure new things can be run (rather than checking these implementation details)?

talked offline. third unit test does that test. The first two unit tests are there to protect against future changes of removing the disposal logic

[pyu10055]

Thanks!

Reviewable status: complete! 2 of 1 approvals obtained (waiting on @pyu10055)