Dialog scroll-lock bugfix

[tompng]

When calling dialog.destroy() soon after dialog.close(), the whole window gets scroll-locked.
(when destroy() is called before the close transition ends)

this.enableScroll_() cannnot placed inside if(this.isOpen_){}
because this.close() (it turns this.isOpen_ = false;) does not enableScroll_()

destroy() {
  if (this.isOpen_) {
    ...
    // this.enableScroll_(); // can't be here. scroll-lock state is not syncrhonized with the flag `isOpen_`.
  }
  this.enableScroll_();
}

other possibilities

destroy() {
  if (this.isOpen_) {
    ...
    this.enableScroll_(); // can be here. scroll-lock state is syncrhonized with the flag `isOpen_`.
  }
}
close() {
  this.isOpen_ = false;
  ...
  this.enableScroll_(); // add this
}

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[codecov-io]

Codecov Report

Merging #2120 into master will increase coverage by 0.94%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #2120      +/-   ##
==========================================
+ Coverage   98.48%   99.43%   +0.94%     
==========================================
  Files          98       84      -14     
  Lines        4230     3720     -510     
  Branches      537      486      -51     
==========================================
- Hits         4166     3699     -467     
+ Misses         64       21      -43

Impacted Files	Coverage Δ
packages/mdc-dialog/foundation.js	100% <100%> (ø)	⬆️
packages/mdc-textfield/foundation.js	98.19% <0%> (-0.71%)	⬇️
packages/mdc-checkbox/foundation.js	97.39% <0%> (-0.25%)	⬇️
packages/mdc-icon-toggle/index.js	100% <0%> (ø)	⬆️
packages/mdc-select/foundation.js	100% <0%> (ø)	⬆️
packages/mdc-ripple/foundation.js	100% <0%> (ø)	⬆️
packages/mdc-toolbar/constants.js	100% <0%> (ø)	⬆️
packages/mdc-textfield/icon/foundation.js	100% <0%> (ø)	⬆️
packages/mdc-select/index.js	100% <0%> (ø)	⬆️
packages/mdc-checkbox/constants.js	100% <0%> (ø)	⬆️
... and 51 more

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[tompng]

I signed it!

[googlebot]

CLAs look good, thanks!

[williamernest]

@tompng Thanks for submitting this PR. Is there a reason that this.enableScroll_() isn't just moved from the handleTransitionEnd function to line 97, just after 'this.isOpen_ = false;'. It seems like a better place to enable scrolling behavior than to always call it in the destroy function.

[tompng]

@williamernest

to line 97, just after 'this.isOpen_ = false;'.

I agree, fixed.

Little changes is that, scrolling is enabled before closing animation starts(originally, it was enabled after animation ends), but I think it's not a problem.

[williamernest]

LGTM. Thanks for updating this.