Only call .hasResolvedAst in assertions.

pkg/compiler/lib/src/compiler.dart

Index: pkg/compiler/lib/src/compiler.dart
diff --git a/pkg/compiler/lib/src/compiler.dart b/pkg/compiler/lib/src/compiler.dart
index 4aa08fdf8e94844ab8523ea7cfdd9b00b431359f..7dbee2a872b7b85acd659fb9aa7eb053679a8f22 100644
--- a/pkg/compiler/lib/src/compiler.dart
+++ b/pkg/compiler/lib/src/compiler.dart
@@ -1932,15 +1932,12 @@ class _CompilerResolution implements Resolution {
   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