Change the x64 optimizing compiler to stop using the fixed context register rsi.

src/x64/lithium-codegen-x64.h

Index: src/x64/lithium-codegen-x64.h
diff --git a/src/x64/lithium-codegen-x64.h b/src/x64/lithium-codegen-x64.h
index 0622e9d285b03bc4e65258467c25720f139ff00c..45591837efd09325235b86e4224ad36aa20c8d5d 100644
--- a/src/x64/lithium-codegen-x64.h
+++ b/src/x64/lithium-codegen-x64.h
@@ -174,6 +174,7 @@ class LCodeGen BASE_EMBEDDED {
                 RelocInfo::Mode mode,
                 LInstruction* instr);
 
+  // CallRuntime assumes that the context is already in rsi.
   void CallRuntime(const Runtime::Function* function,
                    int num_arguments,
                    LInstruction* instr);
@@ -185,9 +186,12 @@ class LCodeGen BASE_EMBEDDED {
     CallRuntime(function, num_arguments, instr);
   }
 
+  // Call runtime from deferred code, where the context has not yet been
+  // moved to rsi.
   void CallRuntimeFromDeferred(Runtime::FunctionId id,
                                int argc,
-                               LInstruction* instr);
+                               LInstruction* instr,
+                               LOperand* context);
 
 
   // Generate a direct call to a known function.  Expects the function