DevTools: return discovered targets asynchronously.

third_party/WebKit/Source/core/inspector/browser_protocol.json

Index: third_party/WebKit/Source/core/inspector/browser_protocol.json
diff --git a/third_party/WebKit/Source/core/inspector/browser_protocol.json b/third_party/WebKit/Source/core/inspector/browser_protocol.json
index 20068fb27b640018359b555452b6b0ed3f83f7bb..f8d24272d7e8a4c6570e4fbb3def8e146d05380a 100644
--- a/third_party/WebKit/Source/core/inspector/browser_protocol.json
+++ b/third_party/WebKit/Source/core/inspector/browser_protocol.json
@@ -4390,7 +4390,8 @@
                     { "name": "targetInfo", "type": "array", "items": { "$ref": "TargetInfo" } }
                 ],
                 "description": "Returns target information for all potential targets.",
-                "handlers": ["browser"]
+                "handlers": ["browser"],
+                "async": true
             },
             {
                 "name": "attach",
@@ -4398,7 +4399,11 @@
                 "parameters": [
                     {"name": "targetId", "$ref": "TargetID", "description": "Target id." }
                 ],
-                "handlers": ["browser"]
+                "returns": [
+                    { "name": "success", "type": "boolean", "description": "Whether attach succeeded." }
+                ],
+                "handlers": ["browser"],
+                "async": true
             },
             {
                 "name": "detach",