Fix cache corruption in incremental resolver

pkg/analyzer/lib/src/generated/incremental_resolver.dart

Index: pkg/analyzer/lib/src/generated/incremental_resolver.dart
diff --git a/pkg/analyzer/lib/src/generated/incremental_resolver.dart b/pkg/analyzer/lib/src/generated/incremental_resolver.dart
index f102201d4dfc2e118d94d743eaef2679801eae08..0a2b2cd04306211b6bfb83996a72f2eff6d1c974 100644
--- a/pkg/analyzer/lib/src/generated/incremental_resolver.dart
+++ b/pkg/analyzer/lib/src/generated/incremental_resolver.dart
@@ -118,12 +118,14 @@ class DeclarationMatcher extends RecursiveAstVisitor {
       _gatherElements(element);
       node.accept(this);
     } on _DeclarationMismatchException {
+      logger.log("mismatched");
       return DeclarationMatchKind.MISMATCH;
     } finally {
       logger.exit();
     }
     // no API changes
     if (_removedElements.isEmpty && _addedElements.isEmpty) {
+      logger.log("no API changes");
       return DeclarationMatchKind.MATCH;
     }
     // simple API change
@@ -2070,12 +2072,12 @@ class _ElementOffsetUpdater extends GeneralizingElementVisitor {
     if (nameOffset > updateOffset) {
       // TODO(scheglov) make sure that we don't put local variables
       // and functions into the cache at all.
-      if (element is LocalVariableElement ||
-          element is FunctionElement &&
-              element.enclosingElement is ExecutableElement) {
+      try {
+        (element as ElementImpl).nameOffset = nameOffset + updateDelta;
+      } on StateError {

[skybrian, 2016/02/17 01:23:41]

StateError is definitely not the right exception, because Errors should not
normally be caught [1].

Alternatives are to create a new exception (perhaps FrozenHashCodeException) or
avoid using an exception here.

We want to avoid clearing the cache entry if at all possible. I don't know how
to do that without actually calculating the new hashCode to see if it's
different. So perhaps I could add an uncachedHashCode property. This would
require subclasses to override uncachedHashCode instead of hashCode. I'm not
sure everyone will remember to do that. Also it's tricky since we would want to
use the uncached location as well.

So, I think introducing FrozenHashCodeException and sticking with this approach
is simplest.

[1]
https://www.dartlang.org/effective-dart/usage/#dont-explicitly-catch-error-or...

         cache.remove(element);
+        (element as ElementImpl).nameOffset = nameOffset + updateDelta;
       }
-      (element as ElementImpl).nameOffset = nameOffset + updateDelta;
       if (element is ConstVariableElement) {
         ConstVariableElement constVariable = element as ConstVariableElement;
         Expression initializer = constVariable.constantInitializer;