Disable region copy on ARM since it isn't supported

ui/ozone/platform/drm/gpu/screen_manager.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/ozone/platform/drm/gpu/screen_manager.h"
 
 #include <xf86drmMode.h>
 
 #include "third_party/skia/include/core/SkCanvas.h"
 #include "ui/gfx/geometry/point.h"
@@ skipping 296 matching lines @@
         gfx::Rect(controller->origin(), controller->GetModeSize()));
     if (!window)
       continue;
 
     window_to_controller_map[window] = controller;
   }
 
   // Apply the new mapping to all windows.
   for (auto pair : window_map_) {
     auto it = window_to_controller_map.find(pair.second);
+    HardwareDisplayController* controller = nullptr;
     if (it != window_to_controller_map.end())
-      pair.second->SetController(it->second);
-    else
-      pair.second->SetController(nullptr);
+      controller = it->second;
+
+    bool should_enable =
+        controller && pair.second->GetController() != controller;
+    pair.second->SetController(controller);
+
+    // If we're moving windows between controllers modeset the controller
+    // otherwise the controller may be waiting for a page flip while the window
+    // tries to schedule another buffer.
+    if (should_enable)
+      EnableController(controller);
   }
 }
 
 OverlayPlane ScreenManager::GetModesetBuffer(
     HardwareDisplayController* controller,
     const gfx::Rect& bounds) {
   DrmWindow* window = FindWindowAt(bounds);
   if (window) {
     const OverlayPlane* primary = window->GetLastModesetBuffer();
     if (primary && primary->buffer->GetSize() == bounds.size())
@@ skipping 44 matching lines @@
 DrmWindow* ScreenManager::FindWindowAt(const gfx::Rect& bounds) const {
   for (auto pair : window_map_) {
     if (pair.second->bounds() == bounds)
       return pair.second;
   }
 
   return nullptr;
 }
 
 }  // namespace ui