fixes #183, remove our InMemory* in favor of analyzer's impl

lib/src/utils.dart

 // Copyright (c) 2015, 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.
 
 /// Holds a couple utility functions used at various places in the system.
 library dev_compiler.src.utils;
 
 import 'dart:io';
 
 import 'package:path/path.dart' as path;
@@ skipping 415 matching lines @@
 
   if (match(s)) return type;
   return findSupertype(s, match);
 }
 
 SourceSpanWithContext createSpan(
     AnalysisContext context, CompilationUnit unit, int start, int end,
     [Source source]) {
   if (source == null) source = unit.element.source;
   var content = context.getContents(source).data;
+  return createSpanHelper(unit, start, end, source, content);
+}
+
+SourceSpanWithContext createSpanHelper(
+    CompilationUnit unit, int start, int end, Source source, String content) {
   var startLoc = locationForOffset(unit, source.uri, start);
   var endLoc = locationForOffset(unit, source.uri, end);
 
   var lineStart = startLoc.offset - startLoc.column;
   // Find the end of the line. This is not exposed directly on LineInfo, but
   // we can find it pretty easily.
   // TODO(jmesserly): for now we do the simple linear scan. Ideally we can get
   // some help from the LineInfo API.
   var lineInfo = unit.lineInfo;
   int lineEnd = endLoc.offset;
   int unitEnd = unit.endToken.end;
   int lineNum = lineInfo.getLocation(lineEnd).lineNumber;
   while (lineEnd < unitEnd &&
       lineInfo.getLocation(++lineEnd).lineNumber == lineNum);
 
   var text = content.substring(start, end);
   var lineText = content.substring(lineStart, lineEnd);
   return new SourceSpanWithContext(startLoc, endLoc, text, lineText);
 }