Merging r9980 into 3.6 branch (Catch OOM when sparse array join results in too large array).

src/runtime.cc

Index: src/runtime.cc
diff --git a/src/runtime.cc b/src/runtime.cc
index 6cb8d1a2f2d5b4741f47b5fa0fbd0f54698ef5a4..813f98f684a9b4466ef5bb646f8f86e10e8d72a5 100644
--- a/src/runtime.cc
+++ b/src/runtime.cc
@@ -6841,7 +6841,12 @@ RUNTIME_FUNCTION(MaybeObject*, Runtime_SparseJoinWithSeparator) {
   // Find total length of join result.
   int string_length = 0;
   bool is_ascii = separator->IsAsciiRepresentation();
-  int max_string_length = SeqAsciiString::kMaxLength;
+  int max_string_length;
+  if (is_ascii) {
+    max_string_length = SeqAsciiString::kMaxLength;
+  } else {
+    max_string_length = SeqTwoByteString::kMaxLength;
+  }
   bool overflow = false;
   CONVERT_NUMBER_CHECKED(int, elements_length,
                          Int32, elements_array->length());