Don't allow software fallback for UI compositor on CrOS

ui/compositor/compositor.cc

 // Copyright (c) 2012 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/compositor/compositor.h"
 
 #include <algorithm>
 #include <deque>
 
 #include "base/bind.h"
@@ skipping 496 matching lines @@
 void Compositor::Layout() {
   // We're sending damage that will be addressed during this composite
   // cycle, so we don't need to schedule another composite to address it.
   disable_schedule_composite_ = true;
   if (root_layer_)
     root_layer_->SendDamagedRects();
   disable_schedule_composite_ = false;
 }
 
 scoped_ptr<cc::OutputSurface> Compositor::CreateOutputSurface(bool fallback) {
+  // Chrome OS doesn't support falling back to software.
+#if defined(OS_CHROMEOS)

[danakj, 2014/01/06 19:33:06]

Can we keep the #ifdefs out of ui::Compositor and do this in the transport
factory?

[ccameron, 2014/01/06 19:47:02]

Sure -- done!

+  fallback = false;
+#endif
   return ContextFactory::GetInstance()->CreateOutputSurface(this, fallback);
 }
 
 void Compositor::DidCommit() {
   DCHECK(!IsLocked());
   FOR_EACH_OBSERVER(CompositorObserver,
                     observer_list_,
                     OnCompositingDidCommit(this));
 }
 
@@ skipping 98 matching lines @@
     // CompositorObservers to be notified before starting another
     // draw cycle.
     ScheduleDraw();
   }
   FOR_EACH_OBSERVER(CompositorObserver,
                     observer_list_,
                     OnCompositingEnded(this));
 }
 
 }  // namespace ui