Enable passing custom fetch function to BrowserHTTPRequest constructor

[caisq]

Towards fixing tensorflow/tfjs#410

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This change is 

[caisq]

@nsthorat For context: this is the first of two PRs that will fix the issue in which tfjs-node users have to override global.fetch in order to load models via http/https.

[tafsiri]

@caisq a general question about this. Why go the subclassing approach instead of allowing a user to pass a fetch function to the load function?

Reviewable status: 0 of 1 approvals obtained (waiting on @nsthorat)

[caisq]

@tafsiri

The two approaches (subclassing vs. adding a new arg to the constructor of BrowserHTTPRequest should both help us achieve the same goal. But I feel the subclassing approach is a little cleaner because it avoids adding an additional arg toBrowserHTTPRequest constructor.
WDYT?

Reviewable status: 0 of 1 approvals obtained (waiting on @nsthorat)

[nsthorat]

My 2c is that passing a function is more canonical JS than inheritance (and inheritance usually is more confusing anyways). I don't care that much though.

[caisq]

@nsthorat @tafsiri I have updated the PR to add an additional argument to the constructor of BrowserHTTPRequest and the factory function browserHTTPRequest. This has the additional nice property that we need to export one fewer symbol.

Thanks for the suggestion. PTAL.

[caisq]

Gentle ping @ reviewers. I may not have made it clear in the previous comment, but the inheritance pattern has been replaced with the additional arg.

[tafsiri]

Thanks @caisq! LGTM

Reviewed 1 of 4 files at r1, 3 of 3 files at r2.
Reviewable status: 0 of 1 approvals obtained (waiting on @caisq and @nsthorat)

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src/io/browser_http.ts, line 51 at r2 (raw file):

      this.fetchFunc = fetch;
    } else {
      assert(typeof fetchFunc === 'function',  'Not a proper fetch function.');

Consider adding "Must pass a function that matches the signature of [link to fetch docs on MDN]

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src/io/browser_http_test.ts, line 1036 at r2 (raw file):

  });

  it('Subclassing BrowserHTTPRequest and overriding fetchFunc', async () => {

Update test string since not doing the subclassing

[caisq]

Thanks for the review!

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

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src/io/browser_http.ts, line 51 at r2 (raw file):

Previously, tafsiri (Yannick Assogba) wrote…

Consider adding "Must pass a function that matches the signature of [link to fetch docs on MDN]

Done.

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src/io/browser_http_test.ts, line 1036 at r2 (raw file):

Previously, tafsiri (Yannick Assogba) wrote…

Update test string since not doing the subclassing

Done.