Backout part 1 of bug 1195431 (cf841511b71a).

layout/base/nsLayoutUtils.cpp

@@ -3037,25 +3037,6 @@ nsLayoutUtils::CalculateAndSetDisplayPortMargins(nsIScrollableFrame* aScrollFram
       content, presShell, displayportMargins, 0, aRepaintMode);
 }
 
-bool
-nsLayoutUtils::WantDisplayPort(const nsDisplayListBuilder* aBuilder,
-                               nsIFrame* aScrollFrame)
-{
-  nsIScrollableFrame* scrollableFrame = do_QueryFrame(aScrollFrame);
-  if (!scrollableFrame) {
-    return false;
-  }
-
-  // We perform an optimization where we ensure that at least one
-  // async-scrollable frame (i.e. one that WantAsyncScroll()) has a displayport.
-  // If that's not the case yet, and we are async-scrollable, we will get a
-  // displayport.
-  return aBuilder->IsPaintingToWindow() &&
-         nsLayoutUtils::AsyncPanZoomEnabled(aScrollFrame) &&
-         !aBuilder->HaveScrollableDisplayPort() &&
-         scrollableFrame->WantAsyncScroll();
-}
-
 bool
 nsLayoutUtils::GetOrMaybeCreateDisplayPort(nsDisplayListBuilder& aBuilder,
                                            nsIFrame* aScrollFrame,
@@ -3074,7 +3055,17 @@ nsLayoutUtils::GetOrMaybeCreateDisplayPort(nsDisplayListBuilder& aBuilder,
 
   bool haveDisplayPort = GetDisplayPort(content, aOutDisplayport);
 
-  if (WantDisplayPort(&aBuilder, aScrollFrame)) {
+  // We perform an optimization where we ensure that at least one
+  // async-scrollable frame (i.e. one that WantsAsyncScroll()) has a displayport.
+  // If that's not the case yet, and we are async-scrollable, we will get a
+  // displayport.
+  // Note: we only do this in processes where we do subframe scrolling to
+  //       begin with (i.e., not in the parent process on B2G).
+  if (aBuilder.IsPaintingToWindow() &&
+      nsLayoutUtils::AsyncPanZoomEnabled(aScrollFrame) &&
+      !aBuilder.HaveScrollableDisplayPort() &&
+      scrollableFrame->WantAsyncScroll()) {
+
     // If we don't already have a displayport, calculate and set one.
     if (!haveDisplayPort) {
       CalculateAndSetDisplayPortMargins(scrollableFrame, nsLayoutUtils::RepaintMode::DoNotRepaint);

layout/base/nsLayoutUtils.h

@@ -2651,12 +2651,6 @@ public:
   static bool CalculateAndSetDisplayPortMargins(nsIScrollableFrame* aScrollFrame,
                                                 RepaintMode aRepaintMode);
 
-  /**
-   * Return true if GetOrMaybeCreateDisplayPort would create a displayport.
-   */
-  static bool WantDisplayPort(const nsDisplayListBuilder* aBuilder,
-                              nsIFrame* aScrollFrame);
-
   /**
    * Get the display port for |aScrollFrame|'s content. If |aScrollFrame|
    * WantsAsyncScroll() and we don't have a scrollable displayport yet (as

layout/generic/nsGfxScrollFrame.cpp

@@ -2824,13 +2824,6 @@ ClipListsExceptCaret(nsDisplayListCollection* aLists,
   ClipItemsExceptCaret(aLists->Content(), aBuilder, aClipFrame, clip, aUsingDisplayPort);
 }
 
-bool
-ScrollFrameHelper::IsUsingDisplayPort(const nsDisplayListBuilder* aBuilder) const
-{
-  return aBuilder->IsPaintingToWindow() &&
-    nsLayoutUtils::GetDisplayPort(mOuter->GetContent());
-}
-
 void
 ScrollFrameHelper::BuildDisplayList(nsDisplayListBuilder*   aBuilder,
                                     const nsRect&           aDirtyRect,
@@ -2871,7 +2864,8 @@ ScrollFrameHelper::BuildDisplayList(nsDisplayListBuilder*   aBuilder,
   bool createLayersForScrollbars = mIsRoot &&
     mOuter->PresContext()->IsRootContentDocument();
 
-  bool usingDisplayPort = IsUsingDisplayPort(aBuilder);
+  bool usingDisplayPort = aBuilder->IsPaintingToWindow() &&
+    nsLayoutUtils::GetDisplayPort(mOuter->GetContent());
 
   if (aBuilder->GetIgnoreScrollFrame() == mOuter || IsIgnoringViewportClipping()) {
     // Root scrollframes have FrameMetrics and clipping on their container

layout/generic/nsGfxScrollFrame.h

@@ -81,8 +81,6 @@ public:
                            bool                    aCreateLayer,
                            bool                    aPositioned);
 
-  bool IsUsingDisplayPort(const nsDisplayListBuilder* aBuilder) const;
-
   bool GetBorderRadii(const nsSize& aFrameSize, const nsSize& aBorderArea,
                       Sides aSkipSides, nscoord aRadii[8]) const;