Code hints are not displayed correctly when auto-scrolling to the right

[redmunds]

1. Create a CSS rule with all properties and values on same line
2. Keeping typing properties and values until page starts to scroll to the right
3. For the next property name, type: b
4. Verify that code hints are displayed and filtered correctly
5. Type: o

Results:
Code Hints are dismissed

Expected:
Code HInts are continues to be displayed and filtered on "bo".

Note that if you continue to type a property name such as "border", code hints are displayed for every other character, and dismissed on the next character.

[njx]

Dupe of #3391