ozone: Add overlay candidate implementation that queries support via IPC

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

Index: ui/ozone/platform/drm/gpu/drm_window.cc
diff --git a/ui/ozone/platform/drm/gpu/drm_window.cc b/ui/ozone/platform/drm/gpu/drm_window.cc
index b2f7a460bb2ecbefab95a557bdd3600a68f6234b..ac12fe28c7cb78692cea5c8a12b996799949b4f6 100644
--- a/ui/ozone/platform/drm/gpu/drm_window.cc
+++ b/ui/ozone/platform/drm/gpu/drm_window.cc
@@ -25,6 +25,9 @@ namespace {
 #define DRM_CAP_CURSOR_HEIGHT 0x9
 #endif
 
+void EmptyFlipCallback(gfx::SwapResult) {
+}
+
 void UpdateCursorImage(DrmBuffer* cursor, const SkBitmap& image) {
   SkRect damage;
   image.getBounds(&damage);
@@ -139,6 +142,12 @@ bool DrmWindow::SchedulePageFlip(bool is_sync,
   return true;
 }
 
+bool DrmWindow::TestPageFlip(const OverlayPlaneList& planes) {
+  return controller_ &&

[spang, 2015/06/01 19:47:39]

Shouldn't it be

if (!controller_)
  return true;

Flipping an offscreen window is an no-op and cannot fail no matter how many
overlays we have. No point in doing any composition.

[achaulk, 2015/06/01 20:43:08]

Sure? It doesn't really matter what we return

+         controller_->SchedulePageFlip(last_submitted_planes_, true, true,
+                                       base::Bind(&EmptyFlipCallback));
+}
+
 const OverlayPlane* DrmWindow::GetLastModesetBuffer() {
   return OverlayPlane::GetPrimaryPlane(last_submitted_planes_);
 }