[tor-bugs] #18777 [Tor Browser]: restore "black on black constrast fix" to ESR45

[Tor Bug Tracker & Wiki]

#18777: restore "black on black constrast fix" to ESR45
---------------------------------+----------------------
     Reporter:  arthuredelstein  |      Owner:  tbb-team
         Type:  defect           |     Status:  new
     Priority:  Medium           |  Milestone:
    Component:  Tor Browser      |    Version:
     Severity:  Normal           |   Keywords:
Actual Points:                   |  Parent ID:  #15197
       Points:                   |   Reviewer:
      Sponsor:                   |
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 brade and mcs's patch to prevent exposing system colors to CSS and canvas
 was partially upstreamed, but there is another part that needs to be
 rebased to ESR45. Because this task is somewhat more complicated, I am
 creating this ticket.

 It would also be good to have a unit test under Tor Project's control that
 ensures that the upstreamed part and the non-upstreamed part are providing
 complete protection.

 The original patch in TBB/ESR38 is
 8b3d00b982db7a1b3101dc9318c1301bf944b161

 The part upstreamed to mozilla (and now in ESR45) is
 61c6a3b38353835315f2d1b9761de9c95ba83c8d

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/18777>
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