[Ozone-DRI] Fix waiting for page flips in mirror mode

ui/ozone/platform/dri/hardware_display_controller.cc

Index: ui/ozone/platform/dri/hardware_display_controller.cc
diff --git a/ui/ozone/platform/dri/hardware_display_controller.cc b/ui/ozone/platform/dri/hardware_display_controller.cc
index 716ec383a5231d39f99c1fccba951486cf83d0cd..b6a1d0b41f86565341d36b5abcd12fc7fae45bb5 100644
--- a/ui/ozone/platform/dri/hardware_display_controller.cc
+++ b/ui/ozone/platform/dri/hardware_display_controller.cc
@@ -119,7 +119,9 @@ void HardwareDisplayController::WaitForPageFlipEvent() {
   bool has_pending_page_flips = false;
   // Wait for the page-flips to complete.
   for (size_t i = 0; i < crtc_controllers_.size(); ++i) {
-    if (crtc_controllers_[i]->page_flip_pending()) {
+    // Messages do not come in any particular order so we need to make sure the

[alexst (slow to review), 2014/10/09 20:54:40]

This deals with messages from multiple monitors on a crtc in mirrored mode if I
understand it correctly. I think it's a crucial thing to add in a comment here.

[dnicoara, 2014/10/10 13:54:00]

Actually, it can be multiple CRTCs in mirror mode. HandleEvent can process an
event for a different CRTC, so without the while-loop it is possible that it'd
process an event for the second CRTC. Moving to the second CRTC this condition
would fail and it'd end up waiting for 1 event rather than 2.

[alexst (slow to review), 2014/10/10 15:50:55]

Right, I actually like your response better than the comment you left in the
code.

I am just being extra nitty about comments. I know my way around this code, but
it's got subtitles and I still have to open my editor and browse around to
convince myself things do what I understand them to do, which is why I keep
asking for more comments.

+    // flip for the current controller has been processed.
+    while (crtc_controllers_[i]->page_flip_pending()) {
       has_pending_page_flips = true;
       crtc_controllers_[i]->drm()->HandleEvent(drm_event);
     }