rework LocalLibraryContributor to resolve referenced units

pkg/analysis_server/lib/src/services/completion/dart/completion_manager.dart

 // Copyright (c) 2015, 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 services.completion.dart.manager;
 
 import 'dart:async';
 
 import 'package:analysis_server/plugin/protocol/protocol.dart';
 import 'package:analysis_server/src/provisional/completion/completion_core.dart'
@@ skipping 249 matching lines @@
 
     // Gracefully degrade if unit cannot be resolved
     if (resolvedUnit == null) {
       return;
     }
 
     // Recompute the target for the newly resolved unit
     _updateTargets(resolvedUnit);
   }
 
+  @override
+  Future<List<CompilationUnitElement>> resolveUnits() async {
+    checkAborted();
+    LibraryElement libElem = libraryElement;
+    if (libElem == null) {
+      return null;
+    }
+    List<CompilationUnitElement> resolvedUnits = <CompilationUnitElement>[];
+    for (CompilationUnitElement unresolvedUnit in libElem.units) {
+      CompilationUnit unit = await _computeAsync(
+          this,
+          new LibrarySpecificUnit(libElem.source, unresolvedUnit.source),
+          RESOLVED_UNIT3,
+          performance,
+          'resolve library unit');

[Brian Wilkerson, 2016/02/12 20:42:07]

Do we want to checkAborted() after returning from an async call?

[danrubel, 2016/02/12 20:54:23]

Good catch! Done.

+      CompilationUnitElement resolvedUnit = unit?.element;
+      resolvedUnits.add(resolvedUnit);

[Brian Wilkerson, 2016/02/12 20:42:07]

Do we want to check for null before adding the unit to the list? I know we test
for it later, but it might be better to test for it here.

[danrubel, 2016/02/12 20:54:23]

Good idea. Done.

+    }
+    return resolvedUnits;
+  }
+
   /**
    * Update the completion [target] and [dotTarget] based on the given [unit].
    */
   void _updateTargets(CompilationUnit unit) {
     _opType = null;
     dotTarget = null;
     target = new CompletionTarget.forOffset(unit, offset);
     AstNode node = target.containingNode;
     if (node is MethodInvocation) {
       if (identical(node.methodName, target.entity)) {
@@ skipping 155 matching lines @@
               // Replacement range for import URI
               return new ReplacementRange(start, end - start);
             }
           }
         }
       }
     }
     return new ReplacementRange(requestOffset, 0);
   }
 }