Implement canonical name scheme in kernel.

pkg/kernel/lib/text/ast_to_text.dart

Index: pkg/kernel/lib/text/ast_to_text.dart
diff --git a/pkg/kernel/lib/text/ast_to_text.dart b/pkg/kernel/lib/text/ast_to_text.dart
index a0e722740c670be7aacd0a04f5999c75583fdc53..31595a17a9a2f714d077d9a60b1704832e5e9cbc 100644
--- a/pkg/kernel/lib/text/ast_to_text.dart
+++ b/pkg/kernel/lib/text/ast_to_text.dart
@@ -37,11 +37,15 @@ class Disambiguator<T> {
 NameSystem globalDebuggingNames = new NameSystem();
 
 String debugLibraryName(Library node) {
-  return node.name ?? globalDebuggingNames.nameLibrary(node);
+  return node == null
+      ? 'null'
+      : node.name ?? globalDebuggingNames.nameLibrary(node);
 }
 
 String debugClassName(Class node) {
-  return node.name ?? globalDebuggingNames.nameClass(node);
+  return node == null
+      ? 'null'
+      : node.name ?? globalDebuggingNames.nameClass(node);
 }
 
 String debugQualifiedClassName(Class node) {