Don't crash on error at end-of-file.

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 b07672edcd33ddc21bd5d01196ac334c7ca2b4ab..f2058ad02caefcf1486c09f1aef0070a2a6db4ea 100644
--- a/pkg/compiler/lib/src/io/source_file.dart
+++ b/pkg/compiler/lib/src/io/source_file.dart
@@ -137,6 +137,11 @@ abstract class SourceFile implements LineColumnProvider {
     if (colorize == null) {
       colorize = (text) => text;
     }
+    if (end > length) {

[ahe, 2015/11/02 16:55:31]

Add a TODO to turn this into an assertion. If you get the wrong position from,
for example, a patch file this could be very confusing.

[ahe, 2015/11/02 16:56:02]

I meant to say: "consider adding a TODO..."

+      start = length - 1;
+      end = length;
+    }
+
     int lineStart = getLine(start);
     int columnStart = getColumn(lineStart, start);
     int lineEnd = getLine(end);