Commit CL 1428333002 to Blink branch for Dart 1.13

DartScriptDebugServer.h

Index: DartScriptDebugServer.h
===================================================================
--- DartScriptDebugServer.h	(revision 202697)
+++ DartScriptDebugServer.h	(working copy)
@@ -88,7 +88,13 @@
     int removeByValue(T value)
     {
         int handle = m_valueToHandleMap.take(value);
-        m_handleToValueMap.remove(handle);
+        // TODO(alanknight): This is clearly wrong. We should never call this
+        //  with an invalid value, but we are doing so sometimes in isolate
+        // shutdown. We need to track down the underlying cause, but this
+        // is a workaround.
+        if (handle != 0) {
+            m_handleToValueMap.remove(handle);
+        }
         return handle;
     }