Devtools: Create layout editor experiment

Source/devtools/protocol.json

 {
     "version": { "major": "1", "minor": "1" },
     "domains": [{
         "domain": "Inspector",
         "hidden": true,
         "types": [],
         "commands": [
             {
                 "name": "enable",
                 "description": "Enables inspector domain notifications.",
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                 ],
                 "description": "Rectangle."
             },
             {
                 "id": "HighlightConfig",
                 "type": "object",
                 "properties": [
                     { "name": "showInfo", "type": "boolean", "optional": true, "description": "Whether the node info tooltip should be shown (default: false)." },
                     { "name": "showRulers", "type": "boolean", "optional": true, "description": "Whether the rulers should be shown (default: false)." },
                     { "name": "showExtensionLines", "type": "boolean", "optional": true, "description": "Whether the extension lines from node to the rulers should be shown (default: false)." },
+                    { "name": "showLayoutEditor", "type": "boolean", "optional": true, "hidden": true},
                     { "name": "contentColor", "$ref": "RGBA", "optional": true, "description": "The content box highlight fill color (default: transparent)." },
                     { "name": "paddingColor", "$ref": "RGBA", "optional": true, "description": "The padding highlight fill color (default: transparent)." },
                     { "name": "borderColor", "$ref": "RGBA", "optional": true, "description": "The border highlight fill color (default: transparent)." },
                     { "name": "marginColor", "$ref": "RGBA", "optional": true, "description": "The margin highlight fill color (default: transparent)." },
                     { "name": "eventTargetColor", "$ref": "RGBA", "optional": true, "hidden": true, "description": "The event target element highlight fill color (default: transparent)." },
                     { "name": "shapeColor", "$ref": "RGBA", "optional": true, "hidden": true, "description": "The shape outside fill color (default: transparent)." },
                     { "name": "shapeMarginColor", "$ref": "RGBA", "optional": true, "hidden": true, "description": "The shape margin fill color (default: transparent)." }
                 ],
                 "description": "Configuration data for the highlighting of page elements."
             }
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                 "name": "securityStateChanged",
                 "description": "The security state of the page changed.",
                 "parameters": [
                     { "name": "securityState", "$ref": "SecurityState", "description": "Security state." }
                 ],
                 "handlers": ["browser"]
             }
         ]
     }]
 }