Always write the source map even if it is inlined.

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

 // Copyright (c) 2016, 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.
 
 import 'dart:collection' show HashSet, Queue;
 import 'dart:convert' show BASE64, JSON, UTF8;
 import 'dart:io' show File;
 import 'package:analyzer/dart/element/element.dart' show LibraryElement;
 import 'package:analyzer/analyzer.dart'
     show AnalysisError, CompilationUnit, ErrorSeverity;
@@ skipping 418 matching lines @@
     var code = getCode(format, singleOutFile, jsPath, mapPath);
     var c = code.code;
     if (singleOutFile) {
       // In singleOutFile mode we wrap each module in an eval statement to
       // leverage sourceURL to improve the debugging experience when source maps
       // are not enabled.
       c += '\n//# sourceURL=${name}.js\n';
       c = 'eval(${JSON.encode(c)});\n';
     }
     new File(jsPath).writeAsStringSync(c);
-    if (code.sourceMap != null && !options.inlineSourceMap) {
+    // TODO(jacobr): it is a bit strange we are writing the source map to a file
+    // even when options.inlineSourceMap is true. To be consistent perhaps we
+    // should also write a copy of the source file without a sourcemap even when
+    // inlineSourceMap is true.
+    if (code.sourceMap != null) {
       new File(mapPath).writeAsStringSync(JSON.encode(code.sourceMap));
     }
   }
 }
 
 /// The output of compiling a JavaScript module in a particular format.
 class JSModuleCode {
   /// The JavaScript code for this module.
   ///
   /// If a [sourceMap] is available, this will include the `sourceMappingURL`
@@ skipping 24 matching lines @@
 
     // Fall back to a relative path.
     return path.toUri(path.relative(path.fromUri(uri), from: dir)).toString();
   }
   for (int i = 0; i < list.length; i++) {
     list[i] = transformUri(list[i]);
   }
   map['file'] = transformUri(map['file']);
   return map;
 }