Allow esi to be an allocatable register on IA32.

src/ia32/full-codegen-ia32.cc

Index: src/ia32/full-codegen-ia32.cc
diff --git a/src/ia32/full-codegen-ia32.cc b/src/ia32/full-codegen-ia32.cc
index ec5d2c86a423473cd7a4e4a8561da2eae930c914..b108ff92347309c4699c424017330c2f73f83986 100644
--- a/src/ia32/full-codegen-ia32.cc
+++ b/src/ia32/full-codegen-ia32.cc
@@ -614,6 +614,7 @@ void FullCodeGenerator::Move(Slot* dst,
   // Emit the write barrier code if the location is in the heap.
   if (dst->type() == Slot::CONTEXT) {
     int offset = Context::SlotOffset(dst->index());
+    ASSERT(!scratch1.is(esi) && !src.is(esi) && !scratch2.is(esi));
     __ RecordWrite(scratch1, offset, src, scratch2);
   }
 }