Add DCHECK that the script context table do not contain native scripts.

This is to prevent unnecessary script contexts to be created for
native scripts, which could end up with a script context table
containing twenty script contexts for a newly created native context.

R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/1301533002

Cr-Commit-Position: refs/heads/master@{#30188}

src/bootstrapper.cc

@@ -3225,7 +3225,6 @@ Genesis::Genesis(Isolate* isolate,
       native_context()->set_natives_utils_object(
           isolate->heap()->undefined_value());
     }
-
     // The serializer cannot serialize typed arrays. Reset those typed arrays
     // for each new context.
     InitializeBuiltinTypedArrays();
@@ -3235,6 +3234,10 @@ Genesis::Genesis(Isolate* isolate,
     if (!InstallDebuggerNatives()) return;
   }
 
+  // Check that the script context table is empty except for the 'this' binding.
+  // We do not need script contexts for native scripts.
+  DCHECK_EQ(1, native_context()->script_context_table()->used());
+
   result_ = native_context();
 }