Bug 1575097 Part 4: Make nsMediaFeatures::GetDeviceSize return unscaled browser sizes for RDM documents. r=emilio

Differential Revision: https://phabricator.services.mozilla.com/D42986

--HG--
extra : moz-landing-system : lando

layout/style/nsMediaFeatures.cpp

@@ -66,21 +66,20 @@ static nsSize GetSize(const Document* aDocument) {
   return pc->GetVisibleArea().Size();
 }
 
-static bool IsDeviceSizePageSize(const Document* aDocument) {
-  nsIDocShell* docShell = aDocument->GetDocShell();
-  if (!docShell) {
-    return false;
-  }
-  return docShell->GetDeviceSizeIsPageSize();
-}
-
 // A helper for three features below.
 static nsSize GetDeviceSize(const Document* aDocument) {
-  if (nsContentUtils::ShouldResistFingerprinting(aDocument) ||
-      IsDeviceSizePageSize(aDocument)) {
+  if (nsContentUtils::ShouldResistFingerprinting(aDocument)) {
     return GetSize(aDocument);
   }
 
+  // Media queries in documents in an RDM pane should use the simulated
+  // device size.
+  Maybe<CSSIntSize> deviceSize =
+      nsGlobalWindowOuter::GetRDMDeviceSize(*aDocument);
+  if (deviceSize.isSome()) {
+    return CSSPixel::ToAppUnits(deviceSize.value());
+  }
+
   nsPresContext* pc = aDocument->GetPresContext();
   // NOTE(emilio): We should probably figure out how to return an appropriate
   // device size here, though in a multi-screen world that makes no sense