Fix build breakage caused from revision 5341 in Windows.

tools/testing/dart/test_suite.dart

Index: tools/testing/dart/test_suite.dart
===================================================================
--- tools/testing/dart/test_suite.dart	(revision 5351)
+++ tools/testing/dart/test_suite.dart	(working copy)
@@ -698,7 +698,7 @@
 
   String getHtmlName(String filename) {
     return filename.replaceAll('/', '_').replaceAll(':', '_')
-        + configuration['component'] + '.html';
+        .replaceAll('\\', '_') + configuration['component'] + '.html';

[Bill Hesse, 2012/03/13 00:26:22]

OK, but I don't know why we don't fix filename when we first get it, rather than
fixing it at many different later places.  I'll fix this someday.

[Emily Fortuna, 2012/03/13 00:33:51]

I'm fine with fixing it initially -- it's just all the Windows bots were broken
at the time, and I needed to get a fix in quickly before more tests broke.

   }
 
   String get dumpRenderTreeFilename() {