Added showing slow scroll rectangles in Layers panel.

Source/devtools/protocol.json

Index: Source/devtools/protocol.json
diff --git a/Source/devtools/protocol.json b/Source/devtools/protocol.json
index 371cd7906ebe7250d1d4a931799103e5aa94d0a1..57d81f8ac4d69a0fbcb8ac0d142a5ba210a0b9fc 100644
--- a/Source/devtools/protocol.json
+++ b/Source/devtools/protocol.json
@@ -3854,6 +3854,19 @@
                 ]
             },
             {
+                "id": "ScrollRect",
+                "type": "object",
+                "description": "Rectangle that should be scrolled on main thread.",
+                "properties": [
+                    { "name": "x", "type": "number", "description": "Rectangle x coordinate." },
+                    { "name": "y", "type": "number", "description": "Rectangle y coordinate." },
+                    { "name": "width", "type": "number", "description": "Rectangle width." },
+                    { "name": "height", "type": "number", "description": "Rectangle height." },
+                    { "name": "layerId", "$ref": "LayerId", "description": "Parent layer id." },
+                    { "name": "type", "type": "string", "enum": ["RepaintsOnScroll", "TouchEventHandler", "WheelEventHandler"], "description": "Reason for rectangle to be scrolled on the main thread" }
+                ]
+            },
+            {
                 "id": "PaintProfile",
                 "type": "array",
                 "description": "Array of timings, one per paint step.",
@@ -3927,7 +3940,8 @@
             {
                 "name": "layerTreeDidChange",
                 "parameters": [
-                    { "name": "layers", "type": "array", "items": { "$ref": "Layer" }, "optional": true, "description": "Layer tree, absent if not in the comspositing mode." }
+                    { "name": "layers", "type": "array", "items": { "$ref": "Layer" }, "optional": true, "description": "Layer tree, absent if not in the comspositing mode." },
+                    { "name": "scrollRects", "type": "array", "items": { "$ref": "ScrollRect" }, "optional": true, "description": "Rectangles scrolling on main thread only." }
                 ]
             },
             {