Make sure that the context argument of HAdd is never NULL.

src/hydrogen.cc

Index: src/hydrogen.cc
diff --git a/src/hydrogen.cc b/src/hydrogen.cc
index 8e9fe00034964da47b342582dec75cea8cedc16a..1afa6603aaa31a308969e9f7a15ba92e67e7d61f 100644
--- a/src/hydrogen.cc
+++ b/src/hydrogen.cc
@@ -3567,7 +3567,10 @@ class BoundsCheckBbData: public ZoneObject {
        HConstant(new_offset, Representation::Integer32());
     if (*add == NULL) {
       new_constant->InsertBefore(check);
-      *add = new(BasicBlock()->zone()) HAdd(NULL,
+      // Because of the bounds checks elimination algorithm, the index is always
+      // an HAdd or an HSub here, so we can safely cast to an HBinaryOperation.
+      HValue* context = HBinaryOperation::cast(check->index())->context();
+      *add = new(BasicBlock()->zone()) HAdd(context,
                                             original_value,
                                             new_constant);
       (*add)->AssumeRepresentation(representation);