Rename classes, methods and fields when minifying

sdk/lib/_internal/compiler/implementation/js_backend/backend.dart

Index: sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
diff --git a/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart b/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
index 19f85f67fdb033e016e434fc75ad3ca340e38093..19fb96604d9a6c21f231e9ce05a457c61abdbbcf 100644
--- a/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
+++ b/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
@@ -672,10 +672,8 @@ class JavaScriptBackend extends Backend {
     return <CompilerTask>[builder, optimizer, generator, emitter];
   }
 
-  JavaScriptBackend(Compiler compiler,
-                    bool generateSourceMap,
-                    bool disableEval)
-      : namer = new Namer(compiler),
+  JavaScriptBackend(Compiler compiler, bool generateSourceMap, bool disableEval)
+      : namer = determineNamer(compiler),
         returnInfo = new Map<Element, ReturnInfo>(),
         invalidateAfterCodegen = new List<Element>(),
         interceptors = new Interceptors(compiler),
@@ -690,6 +688,12 @@ class JavaScriptBackend extends Backend {
     fieldTypes = new FieldTypesRegistry(this);
   }
 
+  static Namer determineNamer(Compiler compiler) {
+    return compiler.enableMinification ?
+        new MinifyNamer(compiler) :
+        new Namer(compiler);
+  }
+
   Element get cyclicThrowHelper {
     return compiler.findHelper(const SourceString("throwCyclicInit"));
   }