Added showing slow scroll rectangles in Layers panel.

Source/devtools/protocol.json

 {
     "version": { "major": "1", "minor": "1" },
     "domains": [{
         "domain": "Inspector",
         "hidden": true,
         "types": [],
         "commands": [
             {
                 "name": "enable",
                 "description": "Enables inspector domain notifications."
@@ skipping 3833 matching lines @@
                     { "name": "height", "type": "number", "description": "Layer height." },
                     { "name": "transform", "type": "array", "items": { "type": "number" }, "minItems": 16, "maxItems": 16, "optional": true, "description": "Transformation matrix for layer, default is identity matrix" },
                     { "name": "anchorX", "type": "number", "optional": true, "description": "Transform anchor point X, absent if no transform specified" },
                     { "name": "anchorY", "type": "number", "optional": true, "description": "Transform anchor point Y, absent if no transform specified" },
                     { "name": "anchorZ", "type": "number", "optional": true, "description": "Transform anchor point Z, absent if no transform specified" },
                     { "name": "paintCount", "type": "integer", "description": "Indicates how many time this layer has painted." },
                     { "name": "invisible", "type": "boolean", "optional": true, "description": "Set if layer is not visible." }
                 ]
             },
             {
+                "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", "$ref": "LayerId", "description": "Parent layer id." },
+                    { "name": "type", "type": "string", "enum": ["NonFastScrollable", "TouchEventHandler", "WheelEventHandler"], "description": "Rectangle type." }
+                ]
+            },
+            {
                 "id": "PaintProfile",
                 "type": "array",
                 "description": "Array of timings, one per paint step.",
                 "items": {
                     "type": "number",
                     "description": "A time in seconds since the end of previous step (for the first step, time since painting started)"
                 }
             }
         ],
         "commands": [
@@ skipping 53 matching lines @@
                 "description": "Replays the layer snapshot and returns the resulting bitmap.",
                 "returns": [
                     { "name": "dataURL", "type": "string", "description": "A data: URL for resulting image." }
                 ]
             }
         ],
         "events": [
             {
                 "name": "layerTreeDidChange",
                 "parameters": [
-                    { "name": "layers", "type": "array", "items": { "$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." }
                 ]
             },
             {
                 "name": "layerPainted",
                 "parameters": [
                     { "name": "layerId", "$ref": "LayerId", "description": "The id of the painted layer." },
                     { "name": "clip", "$ref": "DOM.Rect", "description": "Clip rectangle." }
                 ]
             }
         ]
@@ skipping 103 matching lines @@
             {
                 "name": "dataAvailable",
                 "parameters": [
                     {"name": "value", "type": "array", "items": { "$ref": "PowerEvent" }, "description": "List of power events." }
                 ],
                 "handlers": ["browser", "frontend"]
             }
         ]
     }]
 }