Bug 1501665 Part 5: Change UpdateShouldBuildAsyncZoomContainer to check if document is zoomable. r=botond

Also update ScrollFrameHelper::LayoutScrollbars() to correctly handle
overlay scrollbars when zoomed in in RDM.

Differential Revision: https://phabricator.services.mozilla.com/D20591

--HG--
extra : source : 6a84e97d0e62839c3028a3c3ac89cd944f8e39e5

layout/generic/nsGfxScrollFrame.cpp

@@ -5921,10 +5921,11 @@ void ScrollFrameHelper::LayoutScrollbars(nsBoxLayoutState& aState,
 
   bool hasResizer = HasResizer();
   bool scrollbarOnLeft = !IsScrollbarOnRight();
+  bool overlayScrollBars =
+      LookAndFeel::GetInt(LookAndFeel::eIntID_UseOverlayScrollbars) ||
+      presShell->GetDocument()->InRDMPane();
   bool overlayScrollBarsWithZoom =
-      mIsRoot &&
-      LookAndFeel::GetInt(LookAndFeel::eIntID_UseOverlayScrollbars) &&
-      presShell->IsVisualViewportSizeSet();
+      overlayScrollBars && mIsRoot && presShell->IsVisualViewportSizeSet();
 
   nsSize scrollPortClampingSize = mScrollPort.Size();
   double res = 1.0;

layout/painting/nsDisplayList.cpp

@@ -1261,7 +1261,8 @@ AnimatedGeometryRoot* nsDisplayListBuilder::FindAnimatedGeometryRootFor(
 }
 
 void nsDisplayListBuilder::UpdateShouldBuildAsyncZoomContainer() {
-  mBuildAsyncZoomContainer = gfxPrefs::APZAllowZooming() &&
+  Document* document = mReferenceFrame->PresContext()->Document();
+  mBuildAsyncZoomContainer = nsLayoutUtils::AllowZoomingForDocument(document) &&
                              !gfxPrefs::LayoutUseContainersForRootFrames();
 }