Do not check if the number of display is exactly 2.

When a display removal and a display add happens at the same time,
the number of display is actually 3 during the display removal event.
Therefore the check is too strict.

BUG=414394
R=oshima@chromium.org
TEST=the new test case covers

Review URL: https://codereview.chromium.org/650403002

Cr-Commit-Position: refs/heads/master@{#299553}

ash/display/display_manager_unittest.cc

@@ -572,6 +572,36 @@ TEST_F(DisplayManagerTest, TestNativeDisplaysChanged) {
   EXPECT_FALSE(display_manager()->IsMirrored());
 }
 
+// Make sure crash does not happen if add and remove happens at the same time.
+// See: crbug.com/414394
+TEST_F(DisplayManagerTest, DisplayAddRemoveAtTheSameTime) {
+  if (!SupportsMultipleDisplays())
+    return;
+
+  UpdateDisplay("100+0-500x500,0+501-400x400");
+
+  const int64 primary_id = DisplayController::GetPrimaryDisplayId();
+  const int64 secondary_id = ScreenUtil::GetSecondaryDisplay().id();
+
+  DisplayInfo primary_info = display_manager()->GetDisplayInfo(primary_id);
+  DisplayInfo secondary_info = display_manager()->GetDisplayInfo(secondary_id);
+
+  // An id which is different from primary and secondary.
+  const int64 third_id = primary_id + secondary_id;
+
+  DisplayInfo third_info =
+      CreateDisplayInfo(third_id, gfx::Rect(0, 0, 600, 600));
+
+  std::vector<DisplayInfo> display_info_list;
+  display_info_list.push_back(third_info);
+  display_info_list.push_back(secondary_info);
+  display_manager()->OnNativeDisplaysChanged(display_info_list);
+
+  EXPECT_EQ(third_id, DisplayController::GetPrimaryDisplayId());
+  EXPECT_EQ("600x600", GetDisplayForId(third_id).size().ToString());
+  EXPECT_EQ(secondary_id, ScreenUtil::GetSecondaryDisplay().id());
+}
+
 #if defined(OS_WIN)
 // TODO(scottmg): RootWindow doesn't get resized on Windows
 // Ash. http://crbug.com/247916.

ash/screen_util.cc

@@ -73,7 +73,7 @@ gfx::Rect ScreenUtil::ConvertRectFromScreen(aura::Window* window,
 // static
 const gfx::Display& ScreenUtil::GetSecondaryDisplay() {
   DisplayManager* display_manager = GetDisplayManager();
-  CHECK_EQ(2U, display_manager->GetNumDisplays());
+  CHECK_LE(2U, display_manager->GetNumDisplays());
   return display_manager->GetDisplayAt(0).id() ==
       Shell::GetScreen()->GetPrimaryDisplay().id() ?
       display_manager->GetDisplayAt(1) : display_manager->GetDisplayAt(0);