Added dart2js-generated vmstats.dart, to support non-Dartium browsers.

runtime/bin/vmstats/README

Index: runtime/bin/vmstats/README
===================================================================
--- runtime/bin/vmstats/README	(revision 0)
+++ runtime/bin/vmstats/README	(revision 0)
@@ -0,0 +1,13 @@
+This is the VM Stats program built into the Dart executable.
+
+These files are converted into binary resources during the build, and
+linked into the Dart executable so it is self-contained. These resources
+are available via a built-in HTTP server, enabled with the --stats flag.
+
+Since dart2js requires the dart executable, the vm_stats.dart.js file is
+not re-created with the build. Instead, it should be regenerated whenever
+any of the dart files change, and committed with those changes.  To
+regenerate, from this directory run:
+
+  $ ../../../out/ReleaseIA32/dart-sdk/bin/dart2js -ovmstats.dart.js \
+      vmstats.dart