Bug 1879770 Part 1 - Mark IntrinsicScrollbarGutterSizeAtInlineEdges() const. r=emilio

Differential Revision: https://phabricator.services.mozilla.com/D201892

layout/generic/nsGfxScrollFrame.cpp

@@ -1172,7 +1172,7 @@ void nsHTMLScrollFrame::PlaceScrollArea(ScrollReflowInput& aState,
       scrolledArea, ReflowChildFlags::Default);
 }
 
-nscoord nsHTMLScrollFrame::IntrinsicScrollbarGutterSizeAtInlineEdges() {
+nscoord nsHTMLScrollFrame::IntrinsicScrollbarGutterSizeAtInlineEdges() const {
   const bool isVerticalWM = GetWritingMode().IsVertical();
   if (PresContext()->UseOverlayScrollbars()) {
     return 0;

layout/generic/nsGfxScrollFrame.h

@@ -110,7 +110,7 @@ class nsHTMLScrollFrame : public nsContainerFrame,
   // Return the sum of inline-size of the scrollbar gutters (if any) at the
   // inline-start and inline-end edges of the scroll frame (for a potential
   // scrollbar that scrolls in the block axis).
-  nscoord IntrinsicScrollbarGutterSizeAtInlineEdges();
+  nscoord IntrinsicScrollbarGutterSizeAtInlineEdges() const;
 
   // Compute stable scrollbar-gutter from scrollbar-width and scrollbar-gutter
   // properties.