Bug 1509903 part 1 - Make nsTextFrame::IsFrameSelected() 'final' and inline nsIFrame::IsSelected() to de-virtualize the IsFrameSelected() call in some cases. r=emilio

In particular, in nsCharClipDisplayItem::IsSelected() we know that
the frame must be a nsTextFrame (or nsContinuingTextFrame) which
means nsTextFrame::IsFrameSelected() can be called directly now.

layout/generic/nsFrame.cpp

@@ -11030,13 +11030,6 @@ nsIFrame::CreateOwnLayerIfNeeded(nsDisplayListBuilder* aBuilder,
   }
 }
 
-bool
-nsIFrame::IsSelected() const
-{
-  return (GetContent() && GetContent()->IsSelectionDescendant()) ?
-    IsFrameSelected() : false;
-}
-
 bool
 nsIFrame::IsStackingContext(EffectSet* aEffectSet,
                             const nsStyleDisplay* aStyleDisplay,

layout/generic/nsIFrame.h

@@ -3232,7 +3232,10 @@ public:
   /**
    * @returns true if this frame is selected.
    */
-  bool IsSelected() const;
+  bool IsSelected() const {
+    return (GetContent() && GetContent()->IsSelectionDescendant()) ?
+      IsFrameSelected() : false;
+  }
 
   /**
    *  called to discover where this frame, or a parent frame has user-select style

layout/generic/nsTextFrame.h

@@ -704,7 +704,7 @@ protected:
    * Return true if the frame is part of a Selection.
    * Helper method to implement the public IsSelected() API.
    */
-  bool IsFrameSelected() const override;
+  bool IsFrameSelected() const final;
 
   mozilla::UniquePtr<SelectionDetails> GetSelectionDetails();
 

layout/painting/nsDisplayList.cpp

@@ -90,6 +90,7 @@
 #include "nsSVGMaskFrame.h"
 #include "nsTableCellFrame.h"
 #include "nsTableColFrame.h"
+#include "nsTextFrame.h"
 #include "nsSliderFrame.h"
 #include "ClientLayerManager.h"
 #include "mozilla/layers/StackingContextHelper.h"
@@ -9604,6 +9605,18 @@ nsCharClipDisplayItem::ComputeInvalidationRegion(
   }
 }
 
+bool
+nsCharClipDisplayItem::IsSelected() const
+{
+  if (mIsFrameSelected.isNothing()) {
+    MOZ_ASSERT((nsTextFrame*)do_QueryFrame(mFrame));
+    auto* f = static_cast<nsTextFrame*>(mFrame);
+    mIsFrameSelected.emplace(f->IsSelected());
+  }
+
+  return mIsFrameSelected.value();
+}
+
 nsDisplayEffectsBase::nsDisplayEffectsBase(
   nsDisplayListBuilder* aBuilder,
   nsIFrame* aFrame,

layout/painting/nsDisplayList.h

@@ -7798,14 +7798,7 @@ public:
              : nullptr;
   }
 
-  bool IsSelected() const
-  {
-    if (mIsFrameSelected.isNothing()) {
-      mIsFrameSelected.emplace(mFrame->IsSelected());
-    }
-
-    return mIsFrameSelected.value();
-  }
+  bool IsSelected() const;
 
   // Lengths measured from the visual inline start and end sides
   // (i.e. left and right respectively in horizontal writing modes,