Fix protocol.json ("true" => true), as introduced in r146349.

Source/devtools/protocol.json

 {
     "version": { "major": "1", "minor": "0" },
     "domains": [{
         "domain": "Inspector",
         "hidden": true,
         "types": [],
         "commands": [
             {
                 "name": "enable",
                 "description": "Enables inspector domain notifications."
@@ skipping 435 matching lines @@
                 "description": "Capture page screenshot.",
                 "returns": [
                     { "name": "data", "type": "string", "description": "Base64-encoded image data (PNG)." }
                 ]
             },
             {
                 "name": "handleJavaScriptDialog",
                 "description": "Accepts or dismisses a JavaScript initiated dialog (alert, confirm, prompt, or onbeforeunload).",
                 "parameters": [
                     { "name": "accept", "type": "boolean", "description": "Whether to accept or dismiss the dialog." },
-                    { "name": "promptText", "type": "string", "optional": "true", "description": "The text to enter into the dialog prompt before accepting. Used only if this is a prompt dialog." }
+                    { "name": "promptText", "type": "string", "optional": true, "description": "The text to enter into the dialog prompt before accepting. Used only if this is a prompt dialog." }
                 ],
                 "hidden": true
             }
         ],
         "events": [
             {
                 "name": "domContentEventFired",
                 "parameters": [
                     { "name": "timestamp", "type": "number" }
                 ]
@@ skipping 3252 matching lines @@
                 ]
             }
         ],
         "events": [
             {
                 "name": "layerTreeDidChange"
             }
         ]
     }]
 }