Remove unused is_main_frame_layout_view_layer_ in CompositedLayerMapping

In working on https://crrev.com/733649 this unused variable was noticed.

Change-Id: I1ec61c972e9df85cc098b92cea79fe0e5843a92f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2013322
Commit-Queue: Philip Rogers <pdr@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Auto-Submit: Philip Rogers <pdr@chromium.org>
Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#733769}

third_party/blink/renderer/core/paint/compositing/composited_layer_mapping.cc

@@ -188,14 +188,10 @@ static bool NeedsDecorationOutlineLayer(const PaintLayer& paint_layer,
 CompositedLayerMapping::CompositedLayerMapping(PaintLayer& layer)
     : owning_layer_(layer),
       pending_update_scope_(kGraphicsLayerUpdateNone),
-      is_main_frame_layout_view_layer_(false),
       scrolling_contents_are_empty_(false),
       background_paints_onto_scrolling_contents_layer_(false),
       background_paints_onto_graphics_layer_(false),
       draws_background_onto_content_layer_(false) {
-  if (layer.IsRootLayer() && GetLayoutObject().GetFrame()->IsMainFrame())
-    is_main_frame_layout_view_layer_ = true;
-
   CreatePrimaryGraphicsLayer();
 }
 

third_party/blink/renderer/core/paint/compositing/composited_layer_mapping.h

@@ -482,7 +482,6 @@ class CORE_EXPORT CompositedLayerMapping final : public GraphicsLayerClient {
   PhysicalRect composited_bounds_;
 
   unsigned pending_update_scope_ : 2;
-  unsigned is_main_frame_layout_view_layer_ : 1;
 
   unsigned scrolling_contents_are_empty_ : 1;