Add a "librarySource" field to CompilationUnitElementImpl.

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

Index: pkg/analyzer/lib/src/task/dart.dart
diff --git a/pkg/analyzer/lib/src/task/dart.dart b/pkg/analyzer/lib/src/task/dart.dart
index 9a7b213d49e940a2b5c7b6b6e1de601b09967e26..28e75d36f448a01aa5c9acff520c6ee9d5de3a11 100644
--- a/pkg/analyzer/lib/src/task/dart.dart
+++ b/pkg/analyzer/lib/src/task/dart.dart
@@ -628,6 +628,7 @@ class BuildCompilationUnitElementTask extends SourceBasedAnalysisTask {
     //
     // Prepare inputs.
     //
+    LibrarySpecificUnit librarySpecificUnit = target;
     Source source = getRequiredSource();
     CompilationUnit unit = getRequiredInput(PARSED_UNIT_INPUT_NAME);
     //
@@ -635,7 +636,8 @@ class BuildCompilationUnitElementTask extends SourceBasedAnalysisTask {
     //
     unit = AstCloner.clone(unit);
     CompilationUnitBuilder builder = new CompilationUnitBuilder();
-    CompilationUnitElement element = builder.buildCompilationUnit(source, unit);
+    CompilationUnitElement element =
+        builder.buildCompilationUnit(source, unit, librarySpecificUnit.library);
     //
     // Record outputs.
     //
@@ -1680,9 +1682,11 @@ class ComputeConstantDependenciesTask extends ElementBasedAnalysisTask {
    * given [target].
    */
   static Map<String, TaskInput> buildInputs(Element target) {
+    CompilationUnitElementImpl unit = target
+        .getAncestor((Element element) => element is CompilationUnitElement);
     return <String, TaskInput>{
       UNIT_INPUT: RESOLVED_UNIT
-          .of(new LibrarySpecificUnit(target.library.source, target.source))
+          .of(new LibrarySpecificUnit(unit.librarySource, target.source))
     };
   }