Update V8 to r3431 as required by WebKit r51976.

Change-Id: I567392c3f8c0a0d5201a4249611ac4ccf468cd5b
diff --git a/src/string-stream.cc b/src/string-stream.cc
index 8c62a45..d1859a2 100644
--- a/src/string-stream.cc
+++ b/src/string-stream.cc
@@ -188,7 +188,7 @@
 void StringStream::PrintObject(Object* o) {
   o->ShortPrint(this);
   if (o->IsString()) {
-    if (String::cast(o)->length() <= String::kMaxMediumStringSize) {
+    if (String::cast(o)->length() <= String::kMaxShortPrintLength) {
       return;
     }
   } else if (o->IsNumber() || o->IsOddball()) {