Only call .hasResolvedAst in assertions.

pkg/compiler/lib/src/compiler.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.
 
 library dart2js.compiler_base;
 
 import 'dart:async' show EventSink, Future;
 
 import '../compiler_new.dart' as api;
 import 'cache_strategy.dart' show CacheStrategy;
@@ skipping 1914 matching lines @@
       return compiler.serialization.hasResolvedAst(element);
     }
     return hasBeenResolved(element.memberContext.declaration) &&
         element.hasResolvedAst;
   }
 
   @override
   ResolvedAst getResolvedAst(ExecutableElement element) {
     assert(invariant(element, element.isDeclaration,
         message: "Element $element must be the declaration."));
-    if (hasResolvedAst(element)) {
-      if (compiler.serialization.isDeserialized(element)) {
-        return compiler.serialization.getResolvedAst(element);
-      }
-      return element.resolvedAst;
-    }
     assert(invariant(element, hasResolvedAst(element),
         message: "ResolvedAst not available for $element."));
-    return null;
+    if (compiler.serialization.isDeserialized(element)) {
+      return compiler.serialization.getResolvedAst(element);
+    }
+    return element.resolvedAst;
   }
 
   @override
   ResolvedAst computeResolvedAst(Element element) {
     ensureResolved(element);
     return getResolvedAst(element);
   }
 
   @override
   bool hasResolutionImpact(Element element) {
@@ skipping 142 matching lines @@
   _ElementScanner(this.scanner);
   void scanLibrary(LibraryElement library) => scanner.scanLibrary(library);
   void scanUnit(CompilationUnitElement unit) => scanner.scan(unit);
 }
 
 class _EmptyEnvironment implements Environment {
   const _EmptyEnvironment();
 
   String valueOf(String key) => null;
 }