Handle missing imports/exports/parts.

sdk/lib/_internal/compiler/implementation/warnings.dart

Index: sdk/lib/_internal/compiler/implementation/warnings.dart
diff --git a/sdk/lib/_internal/compiler/implementation/warnings.dart b/sdk/lib/_internal/compiler/implementation/warnings.dart
index 7950a313c8f4f0c5cab3880b80be103b7e1c7e0c..4d70197e633f6b57d48e6db2f38e74297418a9c9 100644
--- a/sdk/lib/_internal/compiler/implementation/warnings.dart
+++ b/sdk/lib/_internal/compiler/implementation/warnings.dart
@@ -615,6 +615,16 @@ Error: "#{value}" is not a valid Symbol name because is not:
 
   static const MessageKind PACKAGE_ROOT_NOT_SET = const MessageKind(
       'Error: Cannot resolve "#{uri}". Package root has not been set.');
+  
+  static const MessageKind INTERNAL_LIBRARY_FROM = const MessageKind(
+      'Error: Internal library "#{resolvedUri}" is not accessible from '
+      '"#{importingUri}".');
+  
+  static const MessageKind INTERNAL_LIBRARY = const MessageKind(
+      'Error: Internal library "#{resolvedUri}" is not accessible.');
+  
+  static const MessageKind LIBRARY_NOT_FOUND = const MessageKind(
+      'Error: Library not found "#{resolvedUri}".');
 
   static const MessageKind COMPILER_CRASHED = const MessageKind(
       'Error: The compiler crashed when compiling this element.');