Change store buffer overflow check to not rely on the store buffer being (2*Size) aligned.

src/heap/store-buffer.h

Index: src/heap/store-buffer.h
diff --git a/src/heap/store-buffer.h b/src/heap/store-buffer.h
index 9c6eac90b5897bb02fe84bb6e360880c4c42860d..1b3fcb0a98b22ea5bb254c596e5cfe1ab7e1dadb 100644
--- a/src/heap/store-buffer.h
+++ b/src/heap/store-buffer.h
@@ -18,9 +18,8 @@ namespace internal {
 // code. On buffer overflow the slots are moved to the remembered set.
 class StoreBuffer {
  public:
-  static const int kStoreBufferOverflowBit = 1 << (14 + kPointerSizeLog2);
-  static const int kStoreBufferSize = kStoreBufferOverflowBit;
-  static const int kStoreBufferLength = kStoreBufferSize / sizeof(Address);
+  static const int kStoreBufferSize = 1 << (14 + kPointerSizeLog2);
+  static const int kStoreBufferMask = kStoreBufferSize - 1;
 
   static void StoreBufferOverflow(Isolate* isolate);