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

Source/devtools/protocol.json

Index: Source/devtools/protocol.json
diff --git a/Source/devtools/protocol.json b/Source/devtools/protocol.json
index e1244951a4805aabeab5d42d56cf7fb8e3ba254f..9ee9f3647161fe5079596401bca81e0f732986b9 100644
--- a/Source/devtools/protocol.json
+++ b/Source/devtools/protocol.json
@@ -737,7 +737,7 @@
                 "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." },