[crankshaft] There is no guarantee that allocations are folded in Crankshaft.

BUG=chromium:615770
LOG=N

Review-Url: https://codereview.chromium.org/2022743002
Cr-Commit-Position: refs/heads/master@{#36579}

src/crankshaft/hydrogen-instructions.h

@@ -5148,10 +5148,13 @@ inline bool ReceiverObjectNeedsWriteBarrier(HValue* object,
     HAllocate* allocate = HAllocate::cast(object);
     if (allocate->IsAllocationFolded()) {
       HValue* dominator = allocate->allocation_folding_dominator();
-      DCHECK(HAllocate::cast(dominator)->IsAllocationFoldingDominator());
+      // There is no guarantee that all allocations are folded together because
+      // GVN performs a fixpoint.
+      if (HAllocate::cast(dominator)->IsAllocationFoldingDominator()) {
         object = dominator;
       }
     }
+  }
 
   if (object->IsConstant() &&
       HConstant::cast(object)->HasExternalReferenceValue()) {