Introduce extra IC state to record additional feedback from IC-s.

src/type-info.h

Index: src/type-info.h
diff --git a/src/type-info.h b/src/type-info.h
index 98d97def29baf8869eb772a3a443693a501d0ac3..e026e88c0fd4f095c782ddf2e69819086aa9c5f6 100644
--- a/src/type-info.h
+++ b/src/type-info.h
@@ -219,6 +219,12 @@ class TypeInfo {
 };
 
 
+enum StringStubFeedback {
+  DEFAULT_STRING_STUB = 0,
+  STRING_INDEX_OUT_OF_BOUNDS = 1
+};
+
+
 // Forward declarations.
 class Assignment;
 class BinaryOperation;