MIPS: Fix debug mode failures introduced by r15561.

The commit r15561 introduced a lot of debug mode test failures
on MIPS. This change solves these failures by making
the FP-saved version of StoreBufferOverflowStub available
at snapshot time. This stub was added to ARM by commit r14359.

BUG=

Review URL: https://codereview.chromium.org/18238012

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@15564 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/mips/code-stubs-mips.cc

@@ -6960,6 +6960,9 @@ void StoreBufferOverflowStub::GenerateFixedRegStubsAheadOfTime(
     Isolate* isolate) {
   StoreBufferOverflowStub stub1(kDontSaveFPRegs);
   stub1.GetCode(isolate)->set_is_pregenerated(true);
+  // Hydrogen code stubs need stub2 at snapshot time.
+  StoreBufferOverflowStub stub2(kSaveFPRegs);
+  stub2.GetCode(isolate)->set_is_pregenerated(true);
 }