Back/Forward buttons state will be stole by preview pages

[darkdh]

• Did you search for similar issues before submitting this one?
  Yes

• Describe the issue you encountered:
  Can't click the back/forward buttons until I click on the target page. And have to avoid cursor the hover on other pages for preview.

• Platform (Win7, 8, 10? macOS? Linux distro?):
  macOS

• Brave Version (revision SHA):
  0.15.2 preview 2

• Steps to reproduce:

  1. Open a page in tab A and make sure it doesn't contain back/forward state
  2. Search things and click the result in tab B
  3. Hover cursor to tab A and leave preview

• Actual result:
  back/forward button is still in tab A's state

• Expected result:
  When leaving preview, it should restore tab B's back/forward button state. However, we have to click on tab B to regain the state.

• Will the steps above reproduce in a fresh profile? If not what other info can be added?

• Is this an issue in the currently released version?

• Can this issue be consistently reproduced?

• Extra QA steps:
  1.
  2.
  3.

• Screenshot if needed:

Kapture 2017-05-02 at 10.21.24.mp4.zip

• Any related issues:

[NejcZdovc]

closing in favor of #8640