[Webkit-unassigned] [Bug 152608] New: Uncaught Exception: TypeError: undefined is not an object (evaluating 'this._dependencies.has')

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=152608

            Bug ID: 152608
           Summary: Uncaught Exception: TypeError: undefined is not an
                    object (evaluating 'this._dependencies.has')
    Classification: Unclassified
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: All
                OS: All
            Status: NEW
          Severity: Major
          Priority: P2
         Component: Web Inspector
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: dcrousso+webkit at gmail.com
                CC: bburg at apple.com, graouts at webkit.org,
                    joepeck at webkit.org, mattbaker at apple.com,
                    nvasilyev at apple.com, timothy at apple.com,
                    webkit-bug-importer at group.apple.com

Created attachment 268031
  --> https://bugs.webkit.org/attachment.cgi?id=268031&action=review
WIP-148254.diff

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Auto-generated details:

Inspected URL:        http://www.apple.com/
Loading completed:    true
Frontend User Agent:  Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_2) AppleWebKit/602.1.15+ (KHTML, like Gecko)
Uncaught exceptions:
 - TypeError: undefined is not an object (evaluating 'this._dependencies.has') (at VisualStylePropertyEditor.js:534:115)
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* STEPS TO REPRODUCE
1. Apply the attached "WIP-148254.diff" (was working on https://bugs.webkit.org/show_bug.cgi?id=148254)
2. Open the inspector to the body element on "https://www.apple.com/"
3. Open the Visual Styles sidebar panel in the Elements tab
4. Select Style Rules > This Element
5. Open the Layout > Position section
6. Change the value of the select element next to Type from Static (should be greyed out) to Relative
7. Switch to a different selector under Style Rules (confirm that the yellow warning icons disappear from the other editors in the Position section)
8. Switch back to This Element and change the select element next to Type back to Static
9. Switch to a different selector under Style Rules (confirm that the yellow warning icons reappear from the other editors in the Position section)
At this point, one of two things can happen:
 1) Step 9 will result in an error that crashes the inspector.
 2) Step 9 will work just fine (and continue to do so no matter how many times steps 6-9 are repeated).  In this case, simply open inspector^2 and enter the following command into the console to see the error: `WebInspector.cssStyleDetailsSidebarPanel._visualStyleDetailsPanel._groups.position.properties.zIndex._checkDependencies()`

* NOTES