Tweak for escaping in instrumentation.

pkg/analyzer/lib/instrumentation/instrumentation.dart

Index: pkg/analyzer/lib/instrumentation/instrumentation.dart
diff --git a/pkg/analyzer/lib/instrumentation/instrumentation.dart b/pkg/analyzer/lib/instrumentation/instrumentation.dart
index c2c1b96a28abe5800848c945c8d44e58b7b241fd..77547fbee5267f77df30737fd4b219a97465d5e4 100644
--- a/pkg/analyzer/lib/instrumentation/instrumentation.dart
+++ b/pkg/analyzer/lib/instrumentation/instrumentation.dart
@@ -135,7 +135,7 @@ class InstrumentationService {
   }
 
   /**
-   * Write an escaped version of the given [string] to the given [buffer].
+   * Write an escaped version of the given [field] to the given [buffer].
    */
   void _escape(StringBuffer buffer, String field) {
     int index = field.indexOf(':');
@@ -144,7 +144,7 @@ class InstrumentationService {
       return;
     }
     int start = 0;
-    while (index > 0) {
+    while (index >= 0) {
       buffer.write(field.substring(start, index));
       buffer.write('::');
       start = index + 1;