Associate compile-time errors with elements.

pkg/compiler/lib/src/js_backend/backend.dart

 // Copyright (c) 2012, 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.
 
 part of js_backend;
 
 const VERBOSE_OPTIMIZER_HINTS = false;
 
 class JavaScriptItemCompilationContext extends ItemCompilationContext {
   final Set<HInstruction> boundsChecked = new Set<HInstruction>();
@@ skipping 1431 matching lines @@
       enqueueClass(enqueuer, cls, registry);
     }
     for (BackendImpact otherImpact in impact.otherImpacts) {
       enqueueImpact(enqueuer, otherImpact, registry);
     }
   }
 
   WorldImpact codegen(CodegenWorkItem work) {
     Element element = work.element;
     if (compiler.elementHasCompileTimeError(element)) {
-      generatedCode[element] = jsAst.js(
-          "function () { throw new Error('Compile time error in $element') }");
+      DiagnosticMessage message =
+          // If there's more than one error, the first is probably most
+          // informative, as the following errors may be side-effects of the
+          // first error.
+          compiler.elementsWithCompileTimeErrors[element].first;
+      String messageText = message.message.computeMessage();
+      jsAst.LiteralString messageLiteral =
+          js.escapedString("Compile time error in $element: $messageText");
+      generatedCode[element] = js(
+          "function () { throw new Error(#); }", [messageLiteral]);
       return const CodegenImpact();
     }
     var kind = element.kind;
     if (kind == ElementKind.TYPEDEF) {
       return const WorldImpact();
     }
     if (element.isConstructor &&
         element.enclosingClass == helpers.jsNullClass) {
       // Work around a problem compiling JSNull's constructor.
       return const CodegenImpact();
@@ skipping 1544 matching lines @@
 
   @override
   void onImpactUsed(ImpactUseCase impactUse) {
     if (impactUse == DeferredLoadTask.IMPACT_USE && !supportSerialization) {
       // TODO(johnniwinther): Allow emptying when serialization has been
       // performed.
       resolution.emptyCache();
     }
   }
 }