Implement 'topLevelLibraryDeclarations' getter to return all libraries with exported top-level decl…

pkg/analyzer/lib/src/dart/analysis/top_level_declaration.dart

Index: pkg/analyzer/lib/src/dart/analysis/top_level_declaration.dart
diff --git a/pkg/analyzer/lib/src/dart/analysis/top_level_declaration.dart b/pkg/analyzer/lib/src/dart/analysis/top_level_declaration.dart
index 1ec5d068c3d7d21920f4017a3f349692f6e66106..c45e0e0496cd9152b2bbc47926c393d3520f25fc 100644
--- a/pkg/analyzer/lib/src/dart/analysis/top_level_declaration.dart
+++ b/pkg/analyzer/lib/src/dart/analysis/top_level_declaration.dart
@@ -33,7 +33,7 @@ class TopLevelLibraryDeclarations {
   /**
    * Top-level declarations in the export namespace of the library.
    */
-  final List<TopLevelDeclaration> declarations = [];
+  final List<TopLevelDeclaration> declarations;
 
-  TopLevelLibraryDeclarations(this.source);
+  TopLevelLibraryDeclarations(this.source, this.declarations);
 }