Small tweaks for AnalysisDriver and FileState.

pkg/analyzer/lib/src/dart/analysis/driver.dart

Index: pkg/analyzer/lib/src/dart/analysis/driver.dart
diff --git a/pkg/analyzer/lib/src/dart/analysis/driver.dart b/pkg/analyzer/lib/src/dart/analysis/driver.dart
index eb2229ff82ffe6e90ba532c418138bb20a7c419d..8fa1dd5c99c85c5758f4e3efe47b81696975cce6 100644
--- a/pkg/analyzer/lib/src/dart/analysis/driver.dart
+++ b/pkg/analyzer/lib/src/dart/analysis/driver.dart
@@ -70,7 +70,7 @@ class AnalysisDriver {
   /**
    * The version of data format, should be incremented on every format change.
    */
-  static const int DATA_VERSION = 16;
+  static const int DATA_VERSION = 17;
 
   /**
    * The number of exception contexts allowed to write. Once this field is
@@ -1595,6 +1595,9 @@ class _ExceptionState {
   final String contextKey;
 
   _ExceptionState(this.exception, this.stackTrace, this.contextKey);
+
+  @override
+  String toString() => '$exception\n$stackTrace';
 }
 
 /**