Update V8 to r6238 as required by WebKit r75993

Change-Id: I12f638fcdd02d9102abab17d81c23cde63c08f22
diff --git a/src/runtime.h b/src/runtime.h
index 5ecae7e..2fa7438 100644
--- a/src/runtime.h
+++ b/src/runtime.h
@@ -363,7 +363,12 @@
   F(LiveEditCheckAndDropActivations, 2, 1) \
   F(LiveEditCompareStringsLinewise, 2, 1) \
   F(GetFunctionCodePositionFromSource, 2, 1) \
-  F(ExecuteInDebugContext, 2, 1)
+  F(ExecuteInDebugContext, 2, 1) \
+  \
+  F(SetFlags, 1, 1) \
+  F(CollectGarbage, 1, 1) \
+  F(GetHeapUsage, 0, 1)
+
 #else
 #define RUNTIME_FUNCTION_LIST_DEBUGGER_SUPPORT(F)
 #endif