Fix inobject slack tracking for both subclassing and non-subclassing cases.

src/code-stubs.h

Index: src/code-stubs.h
diff --git a/src/code-stubs.h b/src/code-stubs.h
index fb22e49213542778547858b0acc50a64be0a43dc..53439026dae9da9ab458260153e06e411ab335df 100644
--- a/src/code-stubs.h
+++ b/src/code-stubs.h
@@ -2443,6 +2443,7 @@ class ScriptContextFieldStub : public HandlerStub {
                          const ScriptContextTable::LookupResult* lookup_result)
       : HandlerStub(isolate) {
     DCHECK(Accepted(lookup_result));
+    STATIC_ASSERT(kContextIndexBits + kSlotIndexBits <= kSubMinorKeyBits);
     set_sub_minor_key(ContextIndexBits::encode(lookup_result->context_index) |
                       SlotIndexBits::encode(lookup_result->slot_index));
   }
@@ -2459,7 +2460,7 @@ class ScriptContextFieldStub : public HandlerStub {
   }
 
  private:
-  static const int kContextIndexBits = 13;
+  static const int kContextIndexBits = 9;
   static const int kSlotIndexBits = 13;
   class ContextIndexBits : public BitField<int, 0, kContextIndexBits> {};
   class SlotIndexBits