Improve behaviour when we hit a stack overflow / OOM error

runtime/observatory/lib/src/elements/debugger.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library debugger_page_element;
 
 import 'dart:async';
 import 'dart:html';
 import 'dart:math';
 import 'observatory_element.dart';
@@ skipping 1474 matching lines @@
     } else if (_isolate.running) {
       console.print("Isolate is running (type 'pause' to interrupt)");
     } else if (_isolate.pauseEvent != null) {
       _reportPause(_isolate.pauseEvent);
     } else {
       console.print('Isolate is in unknown state');
     }
     warnOutOfDate();
   }
 
-  void _reportIsolateError(Isolate isolate) {
+  void _reportIsolateError(Isolate isolate, String eventKind) {
     if (isolate == null) {
       return;
     }
     DartError error = isolate.error;
     if (error == null) {
       return;
     }
     console.newline();
-    console.printBold('Isolate exited due to an unhandled exception:');
+    if (eventKind == ServiceEvent.kPauseException) {
+      console.printBold('Isolate will exit due to an unhandled exception:');
+    } else {
+      console.printBold('Isolate has exited due to an unhandled exception:');
+    }
     console.print(error.message);
     console.newline();
-    console.printBold("Type 'set break-on-exception Unhandled' to pause the"
-                      " isolate when an unhandled exception occurs.");
-    console.newline();
-    console.printBold("You can make this the default by running with "
-                      "--pause-isolates-on-unhandled-exceptions");
+    if (eventKind == ServiceEvent.kPauseException &&
+        (error.exception.isStackOverflowError ||
+         error.exception.isOutOfMemoryError)) {
+      console.printBold(
+          'When an unhandled stack overflow or OOM exception occurs, the VM '
+          'has run out of memory and cannot keep the stack alive while '
+          'paused.');
+    } else {
+      console.printBold("Type 'set break-on-exception Unhandled' to pause the"
+                        " isolate when an unhandled exception occurs.");
+      console.printBold("You can make this the default by running with "
+                        "--pause-isolates-on-unhandled-exceptions");
+    }
   }
 
   void _reportPause(ServiceEvent event) {
     if (event.kind == ServiceEvent.kPauseStart) {
       console.print(
           "Paused at isolate start "
           "(type 'continue' [F7] or 'step' [F10] to start the isolate')");
     } else if (event.kind == ServiceEvent.kPauseExit) {
       console.print(
           "Paused at isolate exit "
           "(type 'continue' or [F7] to exit the isolate')");
-      _reportIsolateError(isolate);
+      _reportIsolateError(isolate, event.kind);
+    } else if (event.kind == ServiceEvent.kPauseException) {
+      console.print(
+          "Paused at an unhandled exception "
+          "(type 'continue' or [F7] to exit the isolate')");
+      _reportIsolateError(isolate, event.kind);
     } else if (stack['frames'].length > 0) {
       Frame frame = stack['frames'][0];
       var script = frame.location.script;
       script.load().then((_) {
         var line = script.tokenToLine(frame.location.tokenPos);
         var col = script.tokenToCol(frame.location.tokenPos);
         if (event.breakpoint != null) {
           var bpId = event.breakpoint.number;
           console.print('Paused at breakpoint ${bpId} at '
                         '${script.name}:${line}:${col}');
@@ skipping 1119 matching lines @@
         }
       });
   }
 
   void focus() {
     $['textBox'].focus();
   }
 
   DebuggerInputElement.created() : super.created();
 }