Created attachment 268031 [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)
- TypeError: undefined is not an object (evaluating 'this._dependencies.has') (at VisualStylePropertyEditor.js:534:115)
* 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()`
From what I was able to investigate, it looks like the value of `this` inside the arrow function on UserInterface/Views/VisualStylePropertyEditor.js:531 is simply empty (as in when I tried to console.log() the value inside the arrow function the output in the console was just a blank line). Maybe an issue with arrow functions?
Happy new year. We ran into this in https://bugs.webkit.org/show_bug.cgi?id=152471 as well. You can convert it to not use arrow functions, and add a FIXME referencing the JSC bug.
*** This bug has been marked as a duplicate of bug 152497 ***