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The GTK theme draws a different top area depending on if Chrome or the window
manager draws the frame [1].  On themes like KDE's Breeze, these colors can be
very different.  This can cause colors calculated from the frame color (like the
inactive tab text color) to be calculated incorrectly.

This CL caches the system and Chrome frame colors in GtkUi and gets the
appropriate one depending on the user's preferences.

Also fix the GTK2 build.

[1] https://cs.chromium.org/chromium/src/chrome/browser/ui/libgtkui/native_theme_gtk3.cc?rcl=ae5bd514aea0486e53a743ddc2870ac3029eb9b3&l=654

BUG=875844
R=pkasting

Change-Id: Ia3e8065de1f843618277b6c562bb9fb54671691d
Reviewed-on: https://chromium-review.googlesource.com/1182508
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584646}