[DevTools] Auto-attach to cross-process subframes under experiment.

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 5931848bd7140cda603874ca25227484101f527c..f5b55c98b63b044f61f6bf34ee1686d6d3e2a944 100644
--- a/third_party/WebKit/Source/core/inspector/browser_protocol.json
+++ b/third_party/WebKit/Source/core/inspector/browser_protocol.json
@@ -3274,7 +3274,7 @@
             {
                 "id": "TargetType",
                 "type": "string",
-                "enum": ["page", "frame", "worker", "service_worker"]
+                "enum": ["page", "iframe", "worker", "service_worker"]
             },
             {
                 "id": "TargetInfo",
@@ -3306,6 +3306,13 @@
                 "handlers": ["browser"]
             },
             {
+                "name": "setAttachToFrames",
+                "parameters": [
+                    { "name": "value", "type": "boolean", "description": "Whether to attach to frames." }
+                ],
+                "handlers": ["browser"]
+            },
+            {
                 "name": "sendMessageToTarget",
                 "parameters": [
                     { "name": "targetId", "type": "string" },