Bug 1916311 - [css-view-transitions] Initial pass at DOM API internals. r=boris,webidl,smaug

This is still fairly incomplete (i.e. no capturing, etc), but it allows
a transition to "start", and then finish (on the next frame always, for
now) or timeout, appropriately.

I think it's in a reviewable shape, given that. There's one known
divergence from the spec, which is described in
w3c/csswg-drafts#10822

Differential Revision: https://phabricator.services.mozilla.com/D220843

Author: emilio

dom/base/Document.cpp

@@ -243,6 +243,7 @@
 #include "mozilla/dom/URL.h"
 #include "mozilla/dom/UseCounterMetrics.h"
 #include "mozilla/dom/UserActivation.h"
+#include "mozilla/dom/ViewTransition.h"
 #include "mozilla/dom/WakeLockJS.h"
 #include "mozilla/dom/WakeLockSentinel.h"
 #include "mozilla/dom/WindowBinding.h"
@@ -2586,6 +2587,7 @@ NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INTERNAL(Document)
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mPrototypeDocument)
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mMidasCommandManager)
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mAll)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mActiveViewTransition)
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mDocGroup)
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mFrameRequestManager)
 
@@ -2715,6 +2717,7 @@ NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(Document)
   NS_IMPL_CYCLE_COLLECTION_UNLINK(mPrototypeDocument)
   NS_IMPL_CYCLE_COLLECTION_UNLINK(mMidasCommandManager)
   NS_IMPL_CYCLE_COLLECTION_UNLINK(mAll)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mActiveViewTransition)
   NS_IMPL_CYCLE_COLLECTION_UNLINK(mReferrerInfo)
   NS_IMPL_CYCLE_COLLECTION_UNLINK(mPreloadReferrerInfo)
 
@@ -17782,10 +17785,49 @@ void Document::ClearStaleServoData() {
   }
 }
 
-ViewTransition* Document::StartViewTransition(
-    const Optional<OwningNonNull<ViewTransitionUpdateCallback>>&) {
-  // TODO(emilio): Not yet implemented
-  return nullptr;
+// https://drafts.csswg.org/css-view-transitions-1/#dom-document-startviewtransition
+already_AddRefed<ViewTransition> Document::StartViewTransition(
+    const Optional<OwningNonNull<ViewTransitionUpdateCallback>>& aCallback) {
+  // Steps 1-3
+  RefPtr transition = new ViewTransition(
+      *this, aCallback.WasPassed() ? &aCallback.Value() : nullptr);
+  if (Hidden()) {
+    // Step 4:
+    //
+    // If document's visibility state is "hidden", then skip transition with an
+    // "InvalidStateError" DOMException, and return transition.
+    transition->SkipTransition(SkipTransitionReason::DocumentHidden);
+    return transition.forget();
+  }
+  if (mActiveViewTransition) {
+    // Step 5:
+    // If document's active view transition is not null, then skip that view
+    // transition with an "AbortError" DOMException in this's relevant Realm.
+    mActiveViewTransition->SkipTransition(
+        SkipTransitionReason::ClobberedActiveTransition);
+  }
+  // Step 6: Set document's active view transition to transition.
+  mActiveViewTransition = transition;
+
+  if (mPresShell) {
+    if (nsRefreshDriver* rd = mPresShell->GetRefreshDriver()) {
+      rd->EnsureViewTransitionOperationsHappen();
+    }
+  }
+  // Step 7: return transition
+  return transition.forget();
+}
+
+void Document::ClearActiveViewTransition() { mActiveViewTransition = nullptr; }
+
+void Document::PerformPendingViewTransitionOperations() {
+  if (mActiveViewTransition) {
+    mActiveViewTransition->PerformPendingOperations();
+  }
+  EnumerateSubDocuments([](Document& aDoc) {
+    aDoc.PerformPendingViewTransitionOperations();
+    return CallState::Continue;
+  });
 }
 
 Selection* Document::GetSelection(ErrorResult& aRv) {

dom/base/Document.h

@@ -3818,8 +3818,13 @@ class Document : public nsINode,
   MOZ_CAN_RUN_SCRIPT void
   DetermineProximityToViewportAndNotifyResizeObservers();
 
-  ViewTransition* StartViewTransition(
+  already_AddRefed<ViewTransition> StartViewTransition(
       const Optional<OwningNonNull<ViewTransitionUpdateCallback>>&);
+  ViewTransition* GetActiveViewTransition() const {
+    return mActiveViewTransition;
+  }
+  void ClearActiveViewTransition();
+  void PerformPendingViewTransitionOperations();
 
   // Getter for PermissionDelegateHandler. Performs lazy initialization.
   PermissionDelegateHandler* GetPermissionDelegateHandler();
@@ -5359,6 +5364,9 @@ class Document : public nsINode,
 
   RefPtr<HTMLAllCollection> mAll;
 
+  // https://drafts.csswg.org/css-view-transitions-1/#document-active-view-transition
+  RefPtr<ViewTransition> mActiveViewTransition;
+
   nsTHashSet<RefPtr<WorkerDocumentListener>> mWorkerListeners;
 
   // Pres shell resolution saved before entering fullscreen mode.