[runtime] Use "the hole" instead of smi 0 as sentinel for context extension.

src/ia32/macro-assembler-ia32.h

Index: src/ia32/macro-assembler-ia32.h
diff --git a/src/ia32/macro-assembler-ia32.h b/src/ia32/macro-assembler-ia32.h
index f615cdff00fcae987d2d3b3a5bb2f5edb1dfaf77..99971b525b1f89cb83f60c5b27af1af6171f9382 100644
--- a/src/ia32/macro-assembler-ia32.h
+++ b/src/ia32/macro-assembler-ia32.h
@@ -85,6 +85,12 @@ class MacroAssembler: public Assembler {
     CompareRoot(with, index);
     j(equal, if_equal, if_equal_distance);
   }
+  void JumpIfRoot(const Operand& with, Heap::RootListIndex index,
+                  Label* if_equal,
+                  Label::Distance if_equal_distance = Label::kNear) {
+    CompareRoot(with, index);
+    j(equal, if_equal, if_equal_distance);
+  }
 
   // Compare the object in a register to a value and jump if they are not equal.
   void JumpIfNotRoot(Register with, Heap::RootListIndex index,
@@ -93,6 +99,12 @@ class MacroAssembler: public Assembler {
     CompareRoot(with, index);
     j(not_equal, if_not_equal, if_not_equal_distance);
   }
+  void JumpIfNotRoot(const Operand& with, Heap::RootListIndex index,
+                     Label* if_not_equal,
+                     Label::Distance if_not_equal_distance = Label::kNear) {
+    CompareRoot(with, index);
+    j(not_equal, if_not_equal, if_not_equal_distance);
+  }
 
   // ---------------------------------------------------------------------------
   // GC Support