Disallow certain blocking DOM calls during microtask execution.

third_party/WebKit/Source/core/frame/Window.idl

Index: third_party/WebKit/Source/core/frame/Window.idl
diff --git a/third_party/WebKit/Source/core/frame/Window.idl b/third_party/WebKit/Source/core/frame/Window.idl
index e79a9b6724fdf7224df849f07c9c6292bd3f0183..08e51507e0019dd6c9226edf69393906bafe1c41 100644
--- a/third_party/WebKit/Source/core/frame/Window.idl
+++ b/third_party/WebKit/Source/core/frame/Window.idl
@@ -72,11 +72,11 @@
     [RuntimeEnabled=ApplicationCache, LogActivity=GetterOnly] readonly attribute ApplicationCache applicationCache;
 
     // user prompts
-    [Measure] void alert();
-    [Measure] void alert(DOMString message);
-    [Measure] boolean confirm(optional DOMString message = "");
-    [Measure] DOMString? prompt(optional DOMString message = "", optional DOMString defaultValue = "");
-    [Measure] void print();
+    [Measure, NotDuringMicrotasks] void alert();
+    [Measure, NotDuringMicrotasks] void alert(DOMString message);
+    [Measure, NotDuringMicrotasks] boolean confirm(optional DOMString message = "");
+    [Measure, NotDuringMicrotasks] DOMString? prompt(optional DOMString message = "", optional DOMString defaultValue = "");
+    [Measure, NotDuringMicrotasks] void print();
 
     [MeasureAs=UnprefixedRequestAnimationFrame] long requestAnimationFrame(FrameRequestCallback callback);
     void cancelAnimationFrame(long handle);