Update V8 to r5091 as required by WebKit r63859.

Change-Id: I8e35d765e6f6c7f89eccff900e1cabe2d5dd6110
diff --git a/src/x64/codegen-x64.h b/src/x64/codegen-x64.h
index b9a3b70..dc6f583 100644
--- a/src/x64/codegen-x64.h
+++ b/src/x64/codegen-x64.h
@@ -521,6 +521,17 @@
                   Condition cc,
                   bool strict,
                   ControlDestination* destination);
+
+  // If at least one of the sides is a constant smi, generate optimized code.
+  void ConstantSmiComparison(Condition cc,
+                             bool strict,
+                             ControlDestination* destination,
+                             Result* left_side,
+                             Result* right_side,
+                             bool left_side_constant_smi,
+                             bool right_side_constant_smi,
+                             bool is_loop_condition);
+
   void GenerateInlineNumberComparison(Result* left_side,
                                       Result* right_side,
                                       Condition cc,
@@ -578,6 +589,7 @@
   void GenerateIsArray(ZoneList<Expression*>* args);
   void GenerateIsRegExp(ZoneList<Expression*>* args);
   void GenerateIsObject(ZoneList<Expression*>* args);
+  void GenerateIsSpecObject(ZoneList<Expression*>* args);
   void GenerateIsFunction(ZoneList<Expression*>* args);
   void GenerateIsUndetectableObject(ZoneList<Expression*>* args);