Bug 1855836 - Make empty threshold list behavior match other browsers…

…. r=smaug

Technically a broken test, but given other browsers' behavior and that
having no thresholds is useless, I don't think this edge-case is worth
fighting about.

See w3c/IntersectionObserver#516 for the spec
change.

Differential Revision: https://phabricator.services.mozilla.com/D189764

dom/base/DOMIntersectionObserver.cpp

@@ -81,8 +81,7 @@ DOMIntersectionObserver::DOMIntersectionObserver(
     dom::IntersectionCallback& aCb)
     : mOwner(aOwner),
       mDocument(mOwner->GetExtantDoc()),
-      mCallback(RefPtr<dom::IntersectionCallback>(&aCb)),
-      mConnected(false) {}
+      mCallback(RefPtr<dom::IntersectionCallback>(&aCb)) {}
 
 already_AddRefed<DOMIntersectionObserver> DOMIntersectionObserver::Constructor(
     const GlobalObject& aGlobal, dom::IntersectionCallback& aCb,
@@ -128,6 +127,9 @@ already_AddRefed<DOMIntersectionObserver> DOMIntersectionObserver::Constructor(
       observer->mThresholds.AppendElement(thresh);
     }
     observer->mThresholds.Sort();
+    if (observer->mThresholds.IsEmpty()) {
+      observer->mThresholds.AppendElement(0.0);
+    }
   } else {
     double thresh = aOptions.mThreshold.GetAsDouble();
     if (thresh < 0.0 || thresh > 1.0) {
@@ -174,8 +176,7 @@ DOMIntersectionObserver::DOMIntersectionObserver(Document& aDocument,
                                                  NativeCallback aCallback)
     : mOwner(aDocument.GetInnerWindow()),
       mDocument(&aDocument),
-      mCallback(aCallback),
-      mConnected(false) {}
+      mCallback(aCallback) {}
 
 already_AddRefed<DOMIntersectionObserver>
 DOMIntersectionObserver::CreateLazyLoadObserver(Document& aDocument) {

dom/base/DOMIntersectionObserver.h

@@ -185,7 +185,7 @@ class DOMIntersectionObserver final : public nsISupports,
   Variant<RefPtr<dom::IntersectionCallback>, NativeCallback> mCallback;
   RefPtr<nsINode> mRoot;
   StyleRect<LengthPercentage> mRootMargin;
-  nsTArray<double> mThresholds;
+  AutoTArray<double, 1> mThresholds;
 
   // These hold raw pointers which are explicitly cleared by UnlinkTarget().
   //
@@ -195,7 +195,7 @@ class DOMIntersectionObserver final : public nsISupports,
   nsTHashSet<Element*> mObservationTargetSet;
 
   nsTArray<RefPtr<DOMIntersectionObserverEntry>> mQueuedEntries;
-  bool mConnected;
+  bool mConnected = false;
 };
 
 NS_DEFINE_STATIC_IID_ACCESSOR(DOMIntersectionObserver,