Fix crash when we don't have a plane to display

ui/ozone/platform/dri/crtc_controller.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/dri/crtc_controller.h"
 
 #include "base/logging.h"
 #include "base/time/time.h"
 #include "ui/ozone/platform/dri/dri_wrapper.h"
 #include "ui/ozone/platform/dri/scanout_buffer.h"
@@ skipping 45 matching lines @@
 
   is_disabled_ = true;
   page_flip_pending_ = false;
   return drm_->DisableCrtc(crtc_);
 }
 
 bool CrtcController::SchedulePageFlip(HardwareDisplayPlaneList* plane_list,
                                       const OverlayPlaneList& overlays) {
   DCHECK(!page_flip_pending_);
   DCHECK(!is_disabled_);
-  const OverlayPlane& primary = OverlayPlane::GetPrimaryPlane(overlays);
-  DCHECK(primary.buffer.get());
+  const OverlayPlane* primary = OverlayPlane::GetPrimaryPlane(overlays);
+  if (!primary) {
+    LOG(ERROR) << "No primary plane to display on crtc " << crtc_;
+    return true;
+  }
+  DCHECK(primary->buffer.get());
 
-  if (primary.buffer->GetSize() != gfx::Size(mode_.hdisplay, mode_.vdisplay)) {
+  if (primary->buffer->GetSize() != gfx::Size(mode_.hdisplay, mode_.vdisplay)) {
     LOG(WARNING) << "Trying to pageflip a buffer with the wrong size. Expected "
                  << mode_.hdisplay << "x" << mode_.vdisplay << " got "
-                 << primary.buffer->GetSize().ToString() << " for"
+                 << primary->buffer->GetSize().ToString() << " for"
                  << " crtc=" << crtc_ << " connector=" << connector_;
     return true;
   }
 
   if (!drm_->plane_manager()->AssignOverlayPlanes(plane_list, overlays, crtc_,
                                                   this)) {
     LOG(ERROR) << "Failed to assign overlay planes for crtc " << crtc_;
     return false;
   }
 
@@ skipping 31 matching lines @@
   cursor_buffer_ = NULL;
   return state;
 }
 
 bool CrtcController::MoveCursor(const gfx::Point& location) {
   DCHECK(!is_disabled_);
   return drm_->MoveCursor(crtc_, location);
 }
 
 }  // namespace ui