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

pkg/compiler/lib/src/io/source_file.dart

Index: pkg/compiler/lib/src/io/source_file.dart
diff --git a/pkg/compiler/lib/src/io/source_file.dart b/pkg/compiler/lib/src/io/source_file.dart
index c8f79cd4c7ac198f3733fa2c068e98b24372c117..8e3c440295f24961b312946c006ea602fc154e16 100644
--- a/pkg/compiler/lib/src/io/source_file.dart
+++ b/pkg/compiler/lib/src/io/source_file.dart
@@ -176,7 +176,10 @@ class Utf8BytesSourceFile extends SourceFile {
 
   Utf8BytesSourceFile(this.uri, this.content);
 
-  String slowText() => UTF8.decode(content);
+  String slowText() {
+    // Don't include the last '0' used by the scanner.
+    return UTF8.decode(content.sublist(0, content.length - 1));
+  }
 
   List<int> slowUtf8Bytes() => content;