Don't crash on deserialized type inference.

pkg/compiler/lib/src/common/resolution.dart

Index: pkg/compiler/lib/src/common/resolution.dart
diff --git a/pkg/compiler/lib/src/common/resolution.dart b/pkg/compiler/lib/src/common/resolution.dart
index e4b1f9fe43f43a566b40beffaf77c98b59b5fa88..0b9f990e91590599e581b845746b18bdba87b66c 100644
--- a/pkg/compiler/lib/src/common/resolution.dart
+++ b/pkg/compiler/lib/src/common/resolution.dart
@@ -14,6 +14,7 @@ import '../elements/elements.dart'
         AstElement,
         ClassElement,
         Element,
+        ExecutableElement,
         FunctionElement,
         FunctionSignature,
         MetadataAnnotation,
@@ -189,10 +190,10 @@ class ListLiteralUse {
 // TODO(johnniwinther): Find a better name for this.
 abstract class Frontend {
   /// Returns `true` if [element] has a [ResolvedAst].
-  bool hasResolvedAst(Element element);
+  bool hasResolvedAst(ExecutableElement element);
 
   /// Returns the `ResolvedAst` for the [element].
-  ResolvedAst getResolvedAst(Element element);
+  ResolvedAst getResolvedAst(ExecutableElement element);
 
   /// Returns the [ResolutionImpact] for [element].
   ResolutionImpact getResolutionImpact(Element element);
@@ -228,10 +229,10 @@ abstract class Resolution implements Frontend {
       Element element, ItemCompilationContext compilationContext);
 
   /// Returns `true` if [element] as a fully computed [ResolvedAst].
-  bool hasResolvedAst(Element element);
+  bool hasResolvedAst(ExecutableElement element);
 
   /// Returns the `ResolvedAst` for the [element].
-  ResolvedAst getResolvedAst(Element element);
+  ResolvedAst getResolvedAst(ExecutableElement element);
 
   /// Returns `true` if the [ResolutionImpact] for [element] is cached.
   bool hasResolutionImpact(Element element);