Implement heap poisoning in ART's Optimizing compiler.

- Instrument ARM, ARM64, x86 and x86-64 code generators.
- Note: To turn heap poisoning on in Optimizing, set the
  environment variable `ART_HEAP_POISONING' to "true"
  before compiling ART.

Bug: 12687968
Change-Id: Ib3120b38cf805a8a50207a314b9ccc90c8d93740
diff --git a/compiler/utils/x86/assembler_x86.cc b/compiler/utils/x86/assembler_x86.cc
index 390d46e..fa85ada 100644
--- a/compiler/utils/x86/assembler_x86.cc
+++ b/compiler/utils/x86/assembler_x86.cc
@@ -1910,12 +1910,12 @@
 }
 
 void X86Assembler::LoadRef(ManagedRegister mdest, ManagedRegister base, MemberOffset offs,
-                           bool poison_reference) {
+                           bool unpoison_reference) {
   X86ManagedRegister dest = mdest.AsX86();
   CHECK(dest.IsCpuRegister() && dest.IsCpuRegister());
   movl(dest.AsCpuRegister(), Address(base.AsX86().AsCpuRegister(), offs));
-  if (kPoisonHeapReferences && poison_reference) {
-    negl(dest.AsCpuRegister());
+  if (unpoison_reference) {
+    MaybeUnpoisonHeapReference(dest.AsCpuRegister());
   }
 }