Add local type inference logic for integer literals.

pkg/front_end/lib/src/fasta/source/source_loader.dart

Index: pkg/front_end/lib/src/fasta/source/source_loader.dart
diff --git a/pkg/front_end/lib/src/fasta/source/source_loader.dart b/pkg/front_end/lib/src/fasta/source/source_loader.dart
index e367dd2830849f3c08714df4b21257006106369b..64447de5ed846088ef9d7b3773905b7f30ece6c9 100644
--- a/pkg/front_end/lib/src/fasta/source/source_loader.dart
+++ b/pkg/front_end/lib/src/fasta/source/source_loader.dart
@@ -126,8 +126,10 @@ class SourceLoader<L> extends Loader<L> {
   }
 
   DietListener createDietListener(LibraryBuilder library) {
-    return new DietListener(library, hierarchy, coreTypes,
-        new KernelTypeInferrer(coreTypes, hierarchy, instrumentation));
+    var typeInferrer = target.strongMode
+        ? new KernelTypeInferrer(coreTypes, hierarchy, instrumentation)
+        : null;
+    return new DietListener(library, hierarchy, coreTypes, typeInferrer);
   }
 
   void resolveParts() {