Add UMA metrics to track user action sequence in VR

third_party/WebKit/Source/modules/vr/VRDisplay.cpp

 // Copyright 2016 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 "modules/vr/VRDisplay.h"
 
 #include "core/css/StylePropertySet.h"
 #include "core/dom/DOMException.h"
 #include "core/dom/FrameRequestCallback.h"
 #include "core/dom/ScriptedAnimationController.h"
@@ skipping 202 matching lines @@
   // updated.
   if (first_present && !UserGestureIndicator::ProcessingUserGesture() &&
       !in_display_activate_) {
     DOMException* exception = DOMException::Create(
         kInvalidStateError, "API can only be initiated by a user gesture.");
     resolver->Reject(exception);
     ReportPresentationResult(PresentationResult::kNotInitiatedByUserGesture);
     return promise;
   }
 
+  // When we are requesting to start presentation with a user action or the
+  // display has activated, record the user action.
+  if (first_present &&

[mthiesse, 2017/05/10 14:58:13]

Why duplicate the logic for when we should (usually) successfully present?

Why not record the action when we call display_->RequestPresent to know that the
page successfully requested presentation.

If you want to also capture failures, why not record an action unconditionally
when the page calls RequestPresent, and another action when successful?

[billorr, 2017/05/10 18:47:13]

I'm trying to filter calls of "requestPresent" to only user actions - which
include putting the device in a headset and clicking to initiate presentation. 
I also filter to the first present because otherwise we are already presenting.

This is almost identitical to the logic above (could be reduced to just
"if(first_present)"), but this appears more clear and future proof if the logic
changes in this function.

I put it here because it is after first_present is defined.  This could be moved
up to the top of the function to get all calls, including those that will fail,
or moved further down to be more likely to indicate success at presenting.  I
don't have a strong preference for either of those, and I think realistically
they should give very similar results.

https://chromium.googlesource.com/chromium/src/+/72a5c913974f7c92e7dc393bf870...

Guidance is to have one event triggered per user action.  This is following that
if we consider clicking "enter vr" and putting the phone in the headset as two
separate actions.

+      (UserGestureIndicator::ProcessingUserGesture() || in_display_activate_)) {
+    Platform::Current()->RecordAction(
+        UserMetricsAction("VR.WebVR.requestPresent"));
+  }
+
   // A valid number of layers must be provided in order to present.
   if (layers.size() == 0 || layers.size() > capabilities_->maxLayers()) {
     ForceExitPresent();
     DOMException* exception =
         DOMException::Create(kInvalidStateError, "Invalid number of layers.");
     resolver->Reject(exception);
     ReportPresentationResult(PresentationResult::kInvalidNumberOfLayers);
     return promise;
   }
 
@@ skipping 431 matching lines @@
       if (layer_.source().isHTMLCanvasElement()) {
         // TODO(klausw,crbug.com/698923): If compositor updates are
         // suppressed, restore them here.
       } else {
         // TODO(junov, crbug.com/695497): Implement for OffscreenCanvas
       }
     } else {
       // Can't get into this presentation mode, so nothing to do here.
     }
     is_presenting_ = false;
+
     OnPresentChange();
+
+    // Record user action for stop presenting.  Note that this could be
+    // user-triggered or not.
+    Platform::Current()->RecordAction(
+        UserMetricsAction("VR.WebVR.StopPresenting"));
   }
 
   rendering_context_ = nullptr;
   context_gl_ = nullptr;
   pending_submit_frame_ = false;
   pending_previous_frame_render_ = false;
 }
 
 void VRDisplay::OnActivate(device::mojom::blink::VRDisplayEventReason reason,
                            const OnActivateCallback& on_handled) {
@@ skipping 182 matching lines @@
   visitor->Trace(stage_parameters_);
   visitor->Trace(eye_parameters_left_);
   visitor->Trace(eye_parameters_right_);
   visitor->Trace(layer_);
   visitor->Trace(rendering_context_);
   visitor->Trace(scripted_animation_controller_);
   visitor->Trace(pending_present_resolvers_);
 }
 
 }  // namespace blink