Warn developers about deprecated features only once per page-load.

Source/devtools/protocol.json

 {
     "version": { "major": "1", "minor": "0" },
     "domains": [{
         "domain": "Inspector",
         "hidden": true,
         "types": [],
         "commands": [
             {
                 "name": "enable",
                 "description": "Enables inspector domain notifications."
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     },
     {
         "domain": "Console",
         "description": "Console domain defines methods and events for interaction with the JavaScript console. Console collects messages created by means of the <a href='http://getfirebug.com/wiki/index.php/Console_API'>JavaScript Console API</a>. One needs to enable this domain using <code>enable</code> command in order to start receiving the console messages. Browser collects messages issued while console domain is not enabled as well and reports them using <code>messageAdded</code> notification upon enabling.",
         "types": [
             {
                 "id": "ConsoleMessage",
                 "type": "object",
                 "description": "Console message.",
                 "properties": [
-                    { "name": "source", "type": "string", "enum": ["xml", "javascript", "network", "console-api", "storage", "appcache", "rendering", "css", "security", "other"], "description": "Message source." },
+                    { "name": "source", "type": "string", "enum": ["xml", "javascript", "network", "console-api", "storage", "appcache", "rendering", "css", "security", "other", "deprecation"], "description": "Message source." },
                     { "name": "level", "type": "string", "enum": ["log", "warning", "error", "debug"], "description": "Message severity." },
                     { "name": "text", "type": "string", "description": "Message text." },
                     { "name": "type", "type": "string", "optional": true, "enum": ["log", "dir", "dirxml", "table", "trace", "clear", "startGroup", "startGroupCollapsed", "endGroup", "assert", "timing", "profile", "profileEnd"], "description": "Console message type." },
                     { "name": "url", "type": "string", "optional": true, "description": "URL of the message origin." },
                     { "name": "line", "type": "integer", "optional": true, "description": "Line number in the resource that generated this message." },
                     { "name": "repeatCount", "type": "integer", "optional": true, "description": "Repeat count for repeated messages." },
                     { "name": "parameters", "type": "array", "items": { "$ref": "Runtime.RemoteObject" }, "optional": true, "description": "Message parameters in case of the formatted message." },
                     { "name": "stackTrace", "$ref": "StackTrace", "optional": true, "description": "JavaScript stack trace for assertions and error messages." },
                     { "name": "networkRequestId", "$ref": "Network.RequestId", "optional": true, "description": "Identifier of the network request associated with this message." }
                 ]
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                 ]
             }
         ],
         "events": [
             {
                 "name": "layerTreeDidChange"
             }
         ]
     }]
 }