Support merged Dart-JS callstacks

Source/devtools/protocol.json

Index: Source/devtools/protocol.json
diff --git a/Source/devtools/protocol.json b/Source/devtools/protocol.json
index fd3a09047335b339c80eaa8a4d1271fe8de0a660..324eb8116ca1b6ed9014ba3aa65d0f06f95fcecb 100644
--- a/Source/devtools/protocol.json
+++ b/Source/devtools/protocol.json
@@ -2962,7 +2962,8 @@
                     { "name": "location", "$ref": "Location", "description": "Location in the source code." },
                     { "name": "scopeChain", "type": "array", "items": { "$ref": "Scope" }, "description": "Scope chain for this call frame." },
                     { "name": "this", "$ref": "Runtime.RemoteObject", "description": "<code>this</code> object for this call frame." },
-                    { "name": "returnValue", "$ref": "Runtime.RemoteObject", "optional": true, "hidden": true, "description": "The value being returned, if the function is at return point." }
+                    { "name": "returnValue", "$ref": "Runtime.RemoteObject", "optional": true, "hidden": true, "description": "The value being returned, if the function is at return point." },
+                    { "name": "timestamp", "type": "number", "optional": true, "description": "Relative ordering of call frames" }
                 ],
                 "description": "JavaScript call frame. Array of call frames form the call stack."
             },