Use AnalysisOptions.signature as a way to check compatibility.

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 5525c3d00ed5b86fae52526ef25b19c9a09c4e42..a6bb7faa147c8accb219d82ed66951f71b165f23 100644
--- a/pkg/analyzer/lib/src/dart/analysis/driver.dart
+++ b/pkg/analyzer/lib/src/dart/analysis/driver.dart
@@ -122,8 +122,7 @@ class AnalysisDriver {
   /**
    * The salt to mix into all hashes used as keys for serialized data.
    */
-  final Uint32List _salt =
-      new Uint32List(1 + AnalysisOptions.crossContextOptionsLength);
+  final Uint32List _salt = new Uint32List(1 + AnalysisOptions.signatureLength);
 
   /**
    * The current file system state.
@@ -820,10 +819,8 @@ class AnalysisDriver {
    */
   void _fillSalt() {
     _salt[0] = DATA_VERSION;
-    List<int> crossContextOptions =
-        _analysisOptions.encodeCrossContextOptions();
-    assert(crossContextOptions.length ==
-        AnalysisOptions.crossContextOptionsLength);
+    List<int> crossContextOptions = _analysisOptions.signature;
+    assert(crossContextOptions.length == AnalysisOptions.signatureLength);
     for (int i = 0; i < crossContextOptions.length; i++) {
       _salt[i + 1] = crossContextOptions[i];
     }