Fire 'stack' getter of error objects after GC.

src/messages.js

Index: src/messages.js
diff --git a/src/messages.js b/src/messages.js
index 0a50ae7861e5e6f1032c4673dfb4aed904db2611..a3cdba620d8bf7121d5a47d3e9d0b0a22d46ae3e 100644
--- a/src/messages.js
+++ b/src/messages.js
@@ -1085,6 +1085,13 @@ function captureStackTrace(obj, cons_opt) {
   var raw_stack = %CollectStackTrace(obj,
                                      cons_opt ? cons_opt : captureStackTrace,
                                      stackTraceLimit);
+
+  // Don't be lazy if the error stack formatting is custom (observable).
+  if (IS_FUNCTION($Error.prepareStackTrace)) {
+    obj.stack = FormatRawStackTrace(obj, raw_stack);
+    return;
+  }
+
   // Note that 'obj' and 'this' maybe different when called on objects that
   // have the error object on its prototype chain.  The getter replaces itself
   // with a data property as soon as the stack trace has been formatted.
@@ -1099,6 +1106,7 @@ function captureStackTrace(obj, cons_opt) {
     %DefineOrRedefineDataProperty(this, 'stack', v, NONE);
   };
 
+  %SetNativeFlag(getter);
   %DefineOrRedefineAccessorProperty(obj, 'stack', getter, setter, DONT_ENUM);
 }
 
@@ -1258,6 +1266,8 @@ function SetUpStackOverflowBoilerplate() {
     %DefineOrRedefineDataProperty(this, 'stack', v, NONE);
   }
 
+  %SetNativeFlag(getter);
+
   %DefineOrRedefineAccessorProperty(
       boilerplate, 'stack', getter, setter, DONT_ENUM);