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

third_party/WebKit/Source/devtools/front_end/main/Main.js

Index: third_party/WebKit/Source/devtools/front_end/main/Main.js
diff --git a/third_party/WebKit/Source/devtools/front_end/main/Main.js b/third_party/WebKit/Source/devtools/front_end/main/Main.js
index e5db6c5da006cc898eaeba93857942ec8f28ffb9..69368f3499b105324adb80734ab95c32248be201 100644
--- a/third_party/WebKit/Source/devtools/front_end/main/Main.js
+++ b/third_party/WebKit/Source/devtools/front_end/main/Main.js
@@ -81,6 +81,7 @@ WebInspector.Main.prototype = {
     {
         Runtime.experiments.register("accessibilityInspection", "Accessibility Inspection");
         Runtime.experiments.register("applyCustomStylesheet", "Allow custom UI themes");
+        Runtime.experiments.register("autoAttachToCrossProcessSubframes", "Auto-attach to cross-process subframes", true);
         Runtime.experiments.register("blackboxJSFramesOnTimeline", "Blackbox JavaScript frames on Timeline", true);
         Runtime.experiments.register("colorContrastRatio", "Contrast ratio line in color picker", true);
         Runtime.experiments.register("continueToFirstInvocation", "Continue to first invocation", true);