Fix data-binding in selected item

[yuriy-fix]

Fixes #128

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This change is 

[tomivirkki]

src/vaadin-dropdown-menu.html, line 355 at r1 (raw file):

          this.addEventListener('iron-resize', this._boundSetPosition);

          const origForwardHostProp = this._overlayElement._instance && this._overlayElement._instance.forwardHostProp;

Why in connectedCallback? _overlayElement is set somewhere else. And its _instance may not be defined.

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Comments from Reviewable

[coveralls]

Pull Request Test Coverage Report for Build 798

• 6 of 6 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.2%) to 96.97%

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Totals
Change from base Build 778:	0.2%
Covered Lines:	111
Relevant Lines:	113

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💛 - Coveralls

[web-padawan]

Review status: 0 of 2 files reviewed, 1 unresolved discussion (waiting on @YuriyVaadin)

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src/vaadin-dropdown-menu.html, line 69 at r1 (raw file):

  <script>
    (function() {
      let memorizedTemplate;

BTW why has this been renamed? "to memoize" is a correct word for this

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Comments from Reviewable

[yuriy-fix]

Review status: 0 of 7 files reviewed, 1 unresolved discussion (waiting on @YuriyVaadin)

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src/vaadin-dropdown-menu.html, line 69 at r1 (raw file):

Previously, web-padawan (Sergey Kulikov) wrote…

BTW why has this been renamed? "to memoize" is a correct word for this

Was thinking it's a typo. Reverted.

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src/vaadin-dropdown-menu.html, line 355 at r1 (raw file):

Previously, tomivirkki (Tomi Virkki) wrote…

Why in connectedCallback? _overlayElement is set somewhere else. And its _instance may not be defined.

Checking it now in ready where the template is assigned to the _overlayElement and it's defined.

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Comments from Reviewable

[tomivirkki]

src/vaadin-dropdown-menu.html, line 355 at r1 (raw file):

Previously, YuriyVaadin (Yuriy Yevstihnyeyev) wrote…

Checking it now in ready where the template is assigned to the _overlayElement and it's defined.

ready isn't the right place for this either. Added a new issue that explains why. Not a blocker for this pr though #138

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Comments from Reviewable

[tomivirkki]

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Reviewed 1 of 2 files at r1, 6 of 6 files at r2.
Review status: complete! all files reviewed, all discussions resolved

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Comments from Reviewable