GitLab

* Add GetDefaultColor() mapping function to make it easy to fix DCHECKs due to
  this code using raw _INCOGNITO color constants but
  ThemeProperties::GetDefaultColor() not expecting them.  This is the change
  that led me to get annoyed and do all the other stuff here.
* Convert typedefs to type aliases.
* Add TP = ThemeProperties type alias for brevity.
* Use =default.
* Mark functions that don't touch member variables "static".
* Fix wrapping issues.
* Because the class here is so long, split it into declaration and definition
  pieces so it's easier to see what's the API and what's helper functions.
* Make the API protected; make helpers private.
* Make data members private.  Add a const accessor for the one member tests use.

Bug: none
Change-Id: I4cc058bb29747cfa84835edbc5ce765401e14527
Reviewed-on: https://chromium-review.googlesource.com/1152108Reviewed-by: Evan Stade <estade@chromium.org>
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578775}