Fix black screen when switching primary display without bounds change

ui/ozone/platform/drm/gpu/drm_window.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/drm_window.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include "base/macros.h"
@@ skipping 105 matching lines @@
 
 void DrmWindow::MoveCursor(const gfx::Point& location) {
   cursor_location_ = location;
 
   if (controller_)
     controller_->MoveCursor(location);
 }
 
 void DrmWindow::SchedulePageFlip(const std::vector<OverlayPlane>& planes,
                                  const SwapCompletionCallback& callback) {
+  if (controller_) {
+    const DrmDevice* drm = controller_->GetAllocationDrmDevice().get();
+    for (const auto& plane : planes) {
+      if (plane.buffer && plane.buffer->GetDrmDevice() != drm) {

[dnicoara, 2016/05/06 19:17:21]

If I understood this correctly this is only required because there may be
in-flight buffers. Could you please add a comment mentioning this. At first this
isn't obvious since |force_buffer_reallocation_| is set to true during the
window bounds update.

[hshi, 2016/05/06 19:22:31]

Done.

+        force_buffer_reallocation_ = true;
+        break;
+      }
+    }
+  }
+
   if (force_buffer_reallocation_) {
     force_buffer_reallocation_ = false;
     callback.Run(gfx::SwapResult::SWAP_NAK_RECREATE_BUFFERS);
     return;
   }
 
   last_submitted_planes_ =
       overlay_validator_->PrepareBuffersForPageFlip(planes);
 
   if (!controller_) {
@@ skipping 103 matching lines @@
       if (!cursor_buffers_[i]->Initialize(
               info, false /* should_register_framebuffer */)) {
         LOG(FATAL) << "Failed to initialize cursor buffer";
         return;
       }
     }
   }
 }
 
 }  // namespace ui