Revert r16648, r16641, r16638 and r16637.

src/mips/codegen-mips.cc

Index: src/mips/codegen-mips.cc
diff --git a/src/mips/codegen-mips.cc b/src/mips/codegen-mips.cc
index e9148ce0aaa2b4c029ec50a150f161262473c3f5..5c847fc8f6227e7896aaacb66163eb244dd59764 100644
--- a/src/mips/codegen-mips.cc
+++ b/src/mips/codegen-mips.cc
@@ -64,8 +64,7 @@ double fast_exp_simulator(double x) {
 UnaryMathFunction CreateExpFunction() {
   if (!FLAG_fast_math) return &exp;
   size_t actual_size;
-  byte* buffer = static_cast<byte*>(VirtualMemory::AllocateRegion(
-          1 * KB, &actual_size, VirtualMemory::EXECUTABLE));
+  byte* buffer = static_cast<byte*>(OS::Allocate(1 * KB, &actual_size, true));
   if (buffer == NULL) return &exp;
   ExternalReference::InitializeMathExpData();
 
@@ -103,9 +102,7 @@ UnaryMathFunction CreateExpFunction() {
   ASSERT(!RelocInfo::RequiresRelocation(desc));
 
   CPU::FlushICache(buffer, actual_size);
-  bool result = VirtualMemory::WriteProtectRegion(buffer, actual_size);
-  ASSERT(result);
-  USE(result);
+  OS::ProtectCode(buffer, actual_size);
 
 #if !defined(USE_SIMULATOR)
   return FUNCTION_CAST<UnaryMathFunction>(buffer);