fix #30591, ensure all extension methods are generated

pkg/dev_compiler/lib/src/compiler/code_generator.dart

Index: pkg/dev_compiler/lib/src/compiler/code_generator.dart
diff --git a/pkg/dev_compiler/lib/src/compiler/code_generator.dart b/pkg/dev_compiler/lib/src/compiler/code_generator.dart
index 8c56a4bef6397a14ac745f0478274c472cc5d504..e2552798ef4753d54ddc48977344feef0937fdb1 100644
--- a/pkg/dev_compiler/lib/src/compiler/code_generator.dart
+++ b/pkg/dev_compiler/lib/src/compiler/code_generator.dart
@@ -963,6 +963,7 @@ class CodeGenerator extends Object
 
     _emitVirtualFieldSymbols(classElem, body);
     _emitClassSignature(methods, allFields, classElem, ctors, className, body);
+    _initExtensionSymbols(classElem, methods, fields);
     _defineExtensionMembers(className, body);
     _emitClassMetadata(node.metadata, className, body);
 
@@ -1982,6 +1983,30 @@ class CodeGenerator extends Object
     }
   }
 
+  /// Ensure `dartx.` symbols we will use are present.
+  void _initExtensionSymbols(ClassElement classElem,
+      List<MethodDeclaration> methods, List<FieldDeclaration> fields) {
+    if (_extensionTypes.hasNativeSubtype(classElem.type)) {
+      for (var m in methods) {
+        if (!m.isAbstract &&
+            !m.isStatic &&
+            resolutionMap.elementDeclaredByMethodDeclaration(m).isPublic) {
+          _declareMemberName(m.element, useExtension: true);

[Jennifer Messerly, 2017/08/31 21:00:48]

FYI, this is mostly the original code, restored from prior to my extension
symbol CL.

The only change is the `_declareMemberName` lines, we used to gather up
non-symbolized names for the `dart.defineExtensionNames` runtime call, now we
just make sure the dartx.<name> is generated.

+        }
+      }
+      for (var fieldDecl in fields) {
+        if (!fieldDecl.isStatic) {
+          for (var field in fieldDecl.fields.variables) {
+            var e = field.element as FieldElement;
+            if (e.isPublic) {
+              _declareMemberName(e.getter, useExtension: true);
+            }
+          }
+        }
+      }
+    }
+  }
+
   /// If a concrete class implements one of our extensions, we might need to
   /// add forwarders.
   void _defineExtensionMembers(