Fix expected PlacementList sort order.

ui/display/display.cc

Index: ui/display/display.cc
diff --git a/ui/display/display.cc b/ui/display/display.cc
index ae0eb5118995c5a124651956c80f9ee9e52ef613..25573f8f9b90e3408ab9234162a0a9b0c92aae70 100644
--- a/ui/display/display.cc
+++ b/ui/display/display.cc
@@ -59,6 +59,17 @@ int64_t internal_display_id_ = -1;
 
 }  // namespace
 
+bool CompareDisplayIds(int64_t id1, int64_t id2) {
+  DCHECK_NE(id1, id2);

[Nico, 2017/07/28 21:09:58]

This DCHECK is not correct. You're passing this to std::sort() which can call
this with the same element for lhs and rhs
(https://stackoverflow.com/questions/38966516/should-sorting-algorithm-pass-sa...).
We're trying to move cros builds to libc++
(https://chromium-review.googlesource.com/c/591775/) and one test fails due to
this incorrect DCHECK. I suppose this should be

  if (id1 == id2) return false;

instead?

+  // Output index is stored in the first 8 bits. See GetDisplayIdFromEDID
+  // in edid_parser.cc.
+  int index_1 = id1 & 0xFF;
+  int index_2 = id2 & 0xFF;
+  DCHECK_NE(index_1, index_2) << id1 << " and " << id2;
+  return Display::IsInternalDisplayId(id1) ||
+         (index_1 < index_2 && !Display::IsInternalDisplayId(id2));
+}
+
 // static
 float Display::GetForcedDeviceScaleFactor() {
   if (g_forced_device_scale_factor < 0)