Fixes for updating synthetic element offsets.

pkg/analyzer/lib/src/task/incremental_element_builder.dart

Index: pkg/analyzer/lib/src/task/incremental_element_builder.dart
diff --git a/pkg/analyzer/lib/src/task/incremental_element_builder.dart b/pkg/analyzer/lib/src/task/incremental_element_builder.dart
index e1f8c5ed49116cf209c1cb8126f6c4b5ad858c5e..54d0ac5252fd56a887594554c21a6103a0582953 100644
--- a/pkg/analyzer/lib/src/task/incremental_element_builder.dart
+++ b/pkg/analyzer/lib/src/task/incremental_element_builder.dart
@@ -130,6 +130,7 @@ class IncrementalCompilationUnitElementBuilder {
    * Fills [unitDelta] with added/remove elements.
    */
   void build() {
+    _materializeLazyElements();
     new CompilationUnitBuilder()
         .buildCompilationUnit(unitSource, newUnit, librarySource);
     _processDirectives();
@@ -170,6 +171,10 @@ class IncrementalCompilationUnitElementBuilder {
     }
   }
 
+  void _materializeLazyElements() {
+    unitElement.accept(new RecursiveElementVisitor());
+  }
+
   ClassElementDelta _processClassMembers(
       ClassDeclaration oldClass, ClassDeclaration newClass) {
     // If the class hierarchy or type parameters are changed,
@@ -683,15 +688,18 @@ class _UpdateElementOffsetsVisitor extends GeneralizingElementVisitor {
     if (element is LibraryElement) {
       return;
     }
-    if (element.isSynthetic && !_isVariableInitializer(element)) {
-      return;
-    }
     if (element is ElementImpl) {
       // name offset
       {
         int oldOffset = element.nameOffset;
         int newOffset = map[oldOffset];
-        assert(newOffset != null);
+        // Some synthetic elements have new offsets, e.g. synthetic accessors
+        // of property inducing elements.  But some are purely synthetic, e.g.
+        // synthetic enum fields and their accessors.
+        if (newOffset == null) {
+          assert(element.isSynthetic);
+          return;
+        }
         element.nameOffset = newOffset;
       }
       // code range
@@ -733,9 +741,4 @@ class _UpdateElementOffsetsVisitor extends GeneralizingElementVisitor {
     }
     super.visitElement(element);
   }
-
-  static bool _isVariableInitializer(Element element) {
-    return element is FunctionElement &&
-        element.enclosingElement is VariableElement;
-  }
 }