MIPS: Minor fixes and additions needed for Turbofan.

src/mips/builtins-mips.cc

Index: src/mips/builtins-mips.cc
diff --git a/src/mips/builtins-mips.cc b/src/mips/builtins-mips.cc
index 2813dd4cdb202ecaf3fd40e0b34255db9a60843e..d8c38a3da75ed6a5ed98f7e94dcc22188d98e619 100644
--- a/src/mips/builtins-mips.cc
+++ b/src/mips/builtins-mips.cc
@@ -45,11 +45,9 @@ void Builtins::Generate_Adaptor(MacroAssembler* masm,
     DCHECK(extra_args == NO_EXTRA_ARGUMENTS);
   }
 
-  // JumpToExternalReference expects s0 to contain the number of arguments
+  // JumpToExternalReference expects a0 to contain the number of arguments
   // including the receiver and the extra arguments.
-  __ Addu(s0, a0, num_extra_args + 1);
-  __ sll(s1, s0, kPointerSizeLog2);
-  __ Subu(s1, s1, kPointerSize);
+  __ Addu(a0, a0, num_extra_args + 1);
   __ JumpToExternalReference(ExternalReference(id, masm->isolate()));
 }