Bug 1760880 - Push document resolution in initial cache. r=morgan

Testing this is hard because the point of failure would be if we
recieved NotifyOfResolutionChange before the IPC doc is constructed.

Differential Revision: https://phabricator.services.mozilla.com/D141904

accessible/generic/LocalAccessible.cpp

@@ -3366,6 +3366,15 @@ already_AddRefed<AccAttributes> LocalAccessible::BundleFieldsForCache(
         mStateFlags &= ~eOldFrameHasValidTransformStyle;
       }
     }
+
+    if (IsDoc()) {
+      if (PresShell* presShell = AsDoc()->PresShellPtr()) {
+        // Send the initial resolution of the document. When this changes, we
+        // will ne notified via nsAS::NotifyOfResolutionChange
+        float resolution = presShell->GetResolution();
+        fields->SetAttribute(nsGkAtoms::resolution, resolution);
+      }
+    }
   }
 
   return fields.forget();

accessible/ipc/RemoteAccessibleBase.cpp

@@ -423,6 +423,7 @@ LayoutDeviceIntRect RemoteAccessibleBase<Derived>::Bounds() const {
             // be scaled relative to its parent doc.
             res = remoteAcc->AsDoc()->mCachedFields->GetAttribute<float>(
                 nsGkAtoms::resolution);
+            MOZ_ASSERT(res, "No cached document resolution found.");
             bounds.ScaleRoundOut(res.valueOr(1.0f));
           }