Remove deprecated sourceMapping syntax.

sdk/lib/_internal/compiler/implementation/js_emitter/code_emitter_task.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.
 
 part of dart2js.js_emitter;
 
 /**
  * Generates the code for all used classes in the program. Static fields (even
  * in classes) are ignored, since they can be treated as non-class elements.
  *
@@ skipping 1652 matching lines @@
       if (backend.requiresPreamble &&
           !backend.htmlLibraryIsLoaded) {
         compiler.reportHint(NO_LOCATION_SPANNABLE, MessageKind.PREAMBLE);
       }
     });
     return compiler.assembledCode;
   }
 
   String generateSourceMapTag(Uri sourceMapUri, Uri fileUri) {
     if (sourceMapUri != null && fileUri != null) {
-      // Using # is the new proposed standard. @ caused problems in Internet
-      // Explorer due to "Conditional Compilation Statements" in JScript,
-      // see:
-      // http://msdn.microsoft.com/en-us/library/7kx09ct1(v=vs.80).aspx
-      // About source maps, see:
-      // https://docs.google.com/a/google.com/document/d/1U1RGAehQwRypUTovF1KRlpiOFze0b-_2gc6fAH0KY0k/edit
-      // TODO(http://dartbug.com/11914): Remove @ line.
       String sourceMapFileName = relativize(fileUri, sourceMapUri, false);
       return '''
 
 //# sourceMappingURL=$sourceMapFileName
-//@ sourceMappingURL=$sourceMapFileName
 ''';
     }
     return '';
   }
 
   ClassBuilder getElementDescriptorForOutputUnit(Element element,
                                                  OutputUnit outputUnit) {
     Map<OutputUnit, ClassBuilder> descriptors =
         elementDescriptors.putIfAbsent(
             element, () => new Map<OutputUnit, ClassBuilder>());
@@ skipping 109 matching lines @@
     for (Element element in compiler.enqueuer.codegen.newlyEnqueuedElements) {
       if (element.isInstanceMember) {
         cachedClassBuilders.remove(element.enclosingClass);
 
         nativeEmitter.cachedBuilders.remove(element.enclosingClass);
 
       }
     }
   }
 }