VR: Fix element visibility checks in the optmimized tree case

Elements are possibly visible only if they ran the opacity computation
step.

BUG=835445
R=mthiesse

Change-Id: Ib45d933c36d509a8d0f224a1d2080fc88de78412
Reviewed-on: https://chromium-review.googlesource.com/1026071Reviewed-by: Michael Thiessen <mthiesse@chromium.org>
Commit-Queue: Christopher Grant <cjgrant@chromium.org>
Cr-Commit-Position: refs/heads/master@{#553199}

chrome/browser/vr/elements/ui_element.cc

@@ -300,10 +300,14 @@ void UiElement::SetVisibleImmediately(bool visible) {
 }
 
 bool UiElement::IsVisible() const {
+  // Many things rely on checking element visibility, including tests.
+  // Therefore, support reporting visibility even if an element sits in an
+  // invisible portion of the tree.  We can infer that if the scene computed
+  // opacities, but this element did not, it must be invisible.
   DCHECK(update_phase_ >= kUpdatedComputedOpacity ||
          FrameLifecycle::phase() >= kUpdatedComputedOpacity);
   // TODO(crbug.com/832216): we shouldn't need to check opacity() here.
-  return update_phase_ != kDirty && opacity() > 0.0f &&
+  return update_phase_ >= kUpdatedComputedOpacity && opacity() > 0.0f &&
          computed_opacity() > 0.0f;
 }
 
@@ -311,7 +315,7 @@ bool UiElement::IsVisibleAndOpaque() const {
   DCHECK(update_phase_ >= kUpdatedComputedOpacity ||
          FrameLifecycle::phase() >= kUpdatedComputedOpacity);
   // TODO(crbug.com/832216): we shouldn't need to check opacity() here.
-  return update_phase_ != kDirty && opacity() == 1.0f &&
+  return update_phase_ >= kUpdatedComputedOpacity && opacity() == 1.0f &&
          computed_opacity() == 1.0f;
 }