Add operators test to source_mapping_test.

pkg/compiler/lib/src/use_unused_api.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /// This file use methods that aren't used by dart2js.dart, but that we wish to
 /// keep anyway. This might be general API that isn't currently in use,
 /// debugging aids, or API only used for testing (see TODO below).
 
 library dart2js.use_unused_api;
 
@@ skipping 266 matching lines @@
   e.lookupInterfaceMember(null);
   n.isAccessibleFrom(null);
   f.reuseElement();
   pce.copyWithEnclosing(null);
   pfe.copyWithEnclosing(null);
   l.forEachImport(null);
 }
 
 useIr(ir_builder.IrBuilder builder) {
   builder
-    ..buildStringConstant(null)
-    ..buildDynamicGet(null, null, null);
+    ..buildStringConstant(null);
 }
 
 useCompiler(dart2jslib.Compiler compiler) {
   compiler.libraryLoader
       ..reset()
       ..resetAsync(null)
       ..lookupLibrary(null);
   compiler.forgetElement(null);
   compiler.backend.constantCompilerTask.copyConstantValues(null);
 }
@@ skipping 29 matching lines @@
 
 class TreeVisitor1 extends tree_ir.ExpressionVisitor1
                       with tree_ir.StatementVisitor1 {
   noSuchMethod(inv) {}
 }
 
 useTreeVisitors() {
   new TreeVisitor1().visitExpression(null, null);
   new TreeVisitor1().visitStatement(null, null);
 }