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When switching modes, we disable CRTCs that do not fit on current freamebuffer,
change framebuffer size, then enable required CRTCs in the right locations.
This fails in a switch from extended desktop to mirror mode, e.g. from
1366x768+1920x1080 to 1024x768 mirrored. Both CRTCs fit into current framebuffer
but they are smaller than the framebuffer we are about to resize to (1024x768)
so XRRSetScreenSize(1024,768) call fails because it cannot shrink framebuffer
size below size of currently enabled CRTCs. The solution is to disable CRTCs
that are bigger than minimum of current and new framebuffer.

BUG=chromium:366280
TEST=switch between mirror and extended desktop on Link or Squawks. Screen size\
(in DISPLAY=:0.0 xrandr --verbose) should shrink when switching to mirror mode.
R=djkurtz@chromium.org
R=oshima@chromium.org
Signed-off-by: Dominik Behr <dbehr@chromium.org>

Review URL: https://codereview.chromium.org/253513002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@266095 0039d316-1c4b-4281-b951-d872f2087c98