Don't include the trailing \0 of input bytes, in the string representation of source files.

Don't include the trailing \0 of input bytes, in the string representation of source files.

The trailing \0 is an artifact of reading the input source into a buffer
of the size + 1. The \0 is then used by the scanner to identify the end
of the file.

BUG=https://code.google.com/p/dart/issues/detail?id=22667

[Anders Johnsen, 2015-03-09 20:55:30]

ajohnsen@google.com changed reviewers:
+ floitsch@google.com

[Anders Johnsen, 2015-03-09 20:55:31]

Feel free to hijack this CL, if there is a better way to fix this.