Add the ability to return descedant event listeners.

third_party/WebKit/Source/devtools/protocol.json

Index: third_party/WebKit/Source/devtools/protocol.json
diff --git a/third_party/WebKit/Source/devtools/protocol.json b/third_party/WebKit/Source/devtools/protocol.json
index f8afcbadebf8d288e8ff2f7bc1f208d0c5cb92c8..bec331b70bad6a9efe8962a3ac327b52306fa496 100644
--- a/third_party/WebKit/Source/devtools/protocol.json
+++ b/third_party/WebKit/Source/devtools/protocol.json
@@ -3919,7 +3919,8 @@
                 "name": "getEventListeners",
                 "hidden": true,
                 "parameters": [
-                    { "name": "objectId", "$ref": "Runtime.RemoteObjectId", "description": "Identifier of the object to return listeners for." }
+                    { "name": "objectId", "$ref": "Runtime.RemoteObjectId", "description": "Identifier of the object to return listeners for." },
+                    { "name": "descendants", "type": "boolean", "optional": true, "description": "If set, also include event listeners on all descendant nodes." }
                 ],
                 "returns": [
                     { "name": "listeners", "type": "array", "items": { "$ref": "EventListener" }, "description": "Array of relevant listeners." }