Fix zero hash handling on ARM.

src/mips/code-stubs-mips.cc

Index: src/mips/code-stubs-mips.cc
===================================================================
--- src/mips/code-stubs-mips.cc	(revision 10360)
+++ src/mips/code-stubs-mips.cc	(working copy)
@@ -5954,7 +5954,7 @@
 
 
 void StringHelper::GenerateHashGetHash(MacroAssembler* masm,
-                                         Register hash) {
+                                       Register hash) {
   // hash += hash << 3;
   __ sll(at, hash, 3);
   __ addu(hash, hash, at);
@@ -5965,12 +5965,11 @@
   __ sll(at, hash, 15);
   __ addu(hash, hash, at);
 
-  uint32_t kHashShiftCutOffMask = (1 << (32 - String::kHashShift)) - 1;
-  __ li(at, Operand(kHashShiftCutOffMask));
+  __ li(at, Operand(String::kHashBitMask));
   __ and_(hash, hash, at);
 
   // if (hash == 0) hash = 27;
-  __ ori(at, zero_reg, 27);
+  __ ori(at, zero_reg, StringHasher::kZeroHash);
   __ movz(hash, at, hash);
 }