MIPS: Do the qNaN fixup at de-serialization time.

src/runtime.cc

Index: src/runtime.cc
diff --git a/src/runtime.cc b/src/runtime.cc
index 3c65d09d2b1dcd06747c54222d65e6e46ef98f41..71a11fa6350aeba48a63ccdb5d606c1d6a960c71 100644
--- a/src/runtime.cc
+++ b/src/runtime.cc
@@ -8406,6 +8406,12 @@ RUNTIME_FUNCTION(MaybeObject*, Runtime_CheckIsBootstrapping) {
 }
 
 
+RUNTIME_FUNCTION(MaybeObject*, Runtime_GetRootNan) {
+  RUNTIME_ASSERT(isolate->bootstrapper()->IsActive());
+  return isolate->heap()->nan_value();
+}
+
+
 RUNTIME_FUNCTION(MaybeObject*, Runtime_Call) {
   HandleScope scope(isolate);
   ASSERT(args.length() >= 2);