Add a flag to show layout shift regions

Add a bool in layer_tree_debug_state. And update the methods
where needed in the cc file.

Declare the flag and its definition in content_switches.

Finally, add the flag in the render_process_host_impl and use it in
the initialization of layer tree settings in render_widget.

Bug: 961846

Change-Id: Ia82da07d65dc5ea829824a077e971b7102e754bb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1603404Reviewed-by: enne <enne@chromium.org>
Reviewed-by: Steve Kobes <skobes@chromium.org>
Reviewed-by: Nicolás Peña Moreno <npm@chromium.org>
Reviewed-by: Antoine Labour <piman@chromium.org>
Commit-Queue: Rasha Nasri <rnasri@google.com>
Cr-Commit-Position: refs/heads/master@{#659660}

cc/debug/layer_tree_debug_state.cc

@@ -12,6 +12,7 @@ namespace cc {
 LayerTreeDebugState::LayerTreeDebugState()
     : show_fps_counter(false),
       show_debug_borders(false),
+      show_layout_shift_regions(false),
       show_paint_rects(false),
       show_property_changed_rects(false),
       show_surface_damage_rects(false),
@@ -49,7 +50,7 @@ bool LayerTreeDebugState::ShowHudRects() const {
          show_surface_damage_rects || show_screen_space_rects ||
          show_touch_event_handler_rects || show_wheel_event_handler_rects ||
          show_scroll_event_handler_rects || show_non_fast_scrollable_rects ||
-         show_layer_animation_bounds_rects;
+         show_layer_animation_bounds_rects || show_layout_shift_regions;
 }
 
 bool LayerTreeDebugState::ShowMemoryStats() const {
@@ -61,6 +62,7 @@ bool LayerTreeDebugState::Equal(const LayerTreeDebugState& a,
   return (
       a.show_fps_counter == b.show_fps_counter &&
       a.show_debug_borders == b.show_debug_borders &&
+      a.show_layout_shift_regions == b.show_layout_shift_regions &&
       a.show_paint_rects == b.show_paint_rects &&
       a.show_property_changed_rects == b.show_property_changed_rects &&
       a.show_surface_damage_rects == b.show_surface_damage_rects &&
@@ -85,6 +87,7 @@ LayerTreeDebugState LayerTreeDebugState::Unite(const LayerTreeDebugState& a,
   r.show_fps_counter |= b.show_fps_counter;
   r.show_debug_borders |= b.show_debug_borders;
 
+  r.show_layout_shift_regions |= b.show_layout_shift_regions;
   r.show_paint_rects |= b.show_paint_rects;
   r.show_property_changed_rects |= b.show_property_changed_rects;
   r.show_surface_damage_rects |= b.show_surface_damage_rects;

cc/debug/layer_tree_debug_state.h

@@ -32,6 +32,7 @@ class CC_DEBUG_EXPORT LayerTreeDebugState {
   bool show_fps_counter;
   DebugBorderTypes show_debug_borders;
 
+  bool show_layout_shift_regions;
   bool show_paint_rects;
   bool show_property_changed_rects;
   bool show_surface_damage_rects;

content/browser/renderer_host/render_process_host_impl.cc

@@ -3018,6 +3018,7 @@ void RenderProcessHostImpl::PropagateBrowserCommandLineToRenderer(
     switches::kRegisterPepperPlugins,
     switches::kRendererStartupDialog,
     switches::kReportVp9AsAnUnsupportedMimeType,
+    switches::kShowLayoutShiftRegions,
     switches::kShowPaintRects,
     switches::kStatsCollectionController,
     switches::kSkiaFontCacheLimitMb,

content/public/common/content_switches.cc

@@ -711,6 +711,10 @@ const char kRendererStartupDialog[]         = "renderer-startup-dialog";
 // Causes the process to run as a sandbox IPC subprocess.
 const char kSandboxIPCProcess[]             = "sandbox-ipc";
 
+// Visibly render a border around layout shift rects in the web page to help
+// debug and study layout shifts.
+const char kShowLayoutShiftRegions[] = "show-layout-shift-regions";
+
 // Visibly render a border around paint rects in the web page to help debug
 // and study painting behavior.
 const char kShowPaintRects[]                = "show-paint-rects";

content/public/common/content_switches.h

@@ -207,6 +207,7 @@ CONTENT_EXPORT extern const char kRendererProcess[];
 CONTENT_EXPORT extern const char kRendererProcessLimit[];
 CONTENT_EXPORT extern const char kRendererStartupDialog[];
 extern const char kSandboxIPCProcess[];
+extern const char kShowLayoutShiftRegions[];
 extern const char kShowPaintRects[];
 CONTENT_EXPORT extern const char kSingleProcess[];
 CONTENT_EXPORT extern const char kSitePerProcess[];

content/renderer/render_widget.cc

@@ -2953,6 +2953,8 @@ cc::LayerTreeSettings RenderWidget::GenerateLayerTreeSettings(
       cmd.HasSwitch(cc::switches::kShowLayerAnimationBounds);
   settings.initial_debug_state.show_paint_rects =
       cmd.HasSwitch(switches::kShowPaintRects);
+  settings.initial_debug_state.show_layout_shift_regions =
+      cmd.HasSwitch(switches::kShowLayoutShiftRegions);
   settings.initial_debug_state.show_property_changed_rects =
       cmd.HasSwitch(cc::switches::kShowPropertyChangedRects);
   settings.initial_debug_state.show_surface_damage_rects =