Bug 1900739 - Remove IsCompositingCheap() r=tnikkel

It's not used since bug 1726291

Differential Revision: https://phabricator.services.mozilla.com/D212649

layout/painting/WindowRenderer.h

@@ -173,8 +173,6 @@ class WindowRenderer : public FrameRecorder {
    */
   virtual void WaitOnTransactionProcessed() {}
 
-  virtual bool IsCompositingCheap() { return true; }
-
   /**
    * returns the maximum texture size on this layer backend, or INT32_MAX
    * if there is no maximum
@@ -261,8 +259,6 @@ class FallbackRenderer : public WindowRenderer {
     name.AssignLiteral("Fallback");
   }
 
-  bool IsCompositingCheap() override { return false; }
-
   void EndTransactionWithColor(const nsIntRect& aRect,
                                const gfx::DeviceColor& aColor);
   void EndTransactionWithList(nsDisplayListBuilder* aBuilder,

layout/painting/nsDisplayList.cpp

@@ -715,7 +715,6 @@ nsDisplayListBuilder::nsDisplayListBuilder(nsIFrame* aReferenceFrame,
       mIsPaintingToWindow(false),
       mUseHighQualityScaling(false),
       mIsPaintingForWebRender(false),
-      mIsCompositingCheap(false),
       mAncestorHasApzAwareEventHandler(false),
       mHaveScrollableDisplayPort(false),
       mWindowDraggingAllowed(false),
@@ -2265,10 +2264,8 @@ void nsDisplayList::PaintRoot(nsDisplayListBuilder* aBuilder, gfxContext* aCtx,
       NS_WARNING("Nowhere to paint into");
       return;
     }
-    bool prevIsCompositingCheap = aBuilder->SetIsCompositingCheap(false);
     Paint(aBuilder, aCtx, presContext->AppUnitsPerDevPixel());
 
-    aBuilder->SetIsCompositingCheap(prevIsCompositingCheap);
     return;
   }
 
@@ -2286,7 +2283,6 @@ void nsDisplayList::PaintRoot(nsDisplayListBuilder* aBuilder, gfxContext* aCtx,
       }
     }
 
-    bool prevIsCompositingCheap = aBuilder->SetIsCompositingCheap(true);
     layerManager->SetTransactionIdAllocator(presContext->RefreshDriver());
 
     bool sent = false;
@@ -2312,7 +2308,6 @@ void nsDisplayList::PaintRoot(nsDisplayListBuilder* aBuilder, gfxContext* aCtx,
                                             aDisplayListBuildTime.valueOr(0.0));
     }
 
-    aBuilder->SetIsCompositingCheap(prevIsCompositingCheap);
     if (presContext->RefreshDriver()->HasScheduleFlush()) {
       presContext->NotifyInvalidation(layerManager->GetLastTransactionId(),
                                       frame->GetRect());
@@ -2331,12 +2326,9 @@ void nsDisplayList::PaintRoot(nsDisplayListBuilder* aBuilder, gfxContext* aCtx,
     }
   }
 
-  bool temp = aBuilder->SetIsCompositingCheap(renderer->IsCompositingCheap());
   fallback->EndTransactionWithList(aBuilder, this,
                                    presContext->AppUnitsPerDevPixel(),
                                    WindowRenderer::END_DEFAULT);
-
-  aBuilder->SetIsCompositingCheap(temp);
 }
 
 void nsDisplayList::DeleteAll(nsDisplayListBuilder* aBuilder) {

layout/painting/nsDisplayList.h

@@ -636,13 +636,6 @@ class nsDisplayListBuilder {
   void SetHaveScrollableDisplayPort() { mHaveScrollableDisplayPort = true; }
   void ClearHaveScrollableDisplayPort() { mHaveScrollableDisplayPort = false; }
 
-  bool SetIsCompositingCheap(bool aCompositingCheap) {
-    bool temp = mIsCompositingCheap;
-    mIsCompositingCheap = aCompositingCheap;
-    return temp;
-  }
-
-  bool IsCompositingCheap() const { return mIsCompositingCheap; }
   /**
    * Display the caret if needed.
    */
@@ -1886,7 +1879,6 @@ class nsDisplayListBuilder {
   bool mIsPaintingToWindow;
   bool mUseHighQualityScaling;
   bool mIsPaintingForWebRender;
-  bool mIsCompositingCheap;
   bool mAncestorHasApzAwareEventHandler;
   // True when the first async-scrollable scroll frame for which we build a
   // display list has a display port. An async-scrollable scroll frame is one