Reduce foot-print of Error.safeToString on strings.

Use existing JSON encoding instead of a custom encoding.
This allows dart2js to use the system JSON stringifier directly.

R=sra@google.com

Review URL: https://codereview.chromium.org//718053003

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@41704 260f80e4-7a28-3924-810f-c04153c831b5
Optimize new error and toStrings for size.

R=sra@google.com

Review URL: https://codereview.chromium.org//720703002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@41705 260f80e4-7a28-3924-810f-c04153c831b5
Mark corelib/regexp/pcre_test as slow on dart2js

Filed issue 21593 to track this

Review URL: https://codereview.chromium.org//718393002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@41706 260f80e4-7a28-3924-810f-c04153c831b5