Add asserts to ensure that we:

src/x64/full-codegen-x64.cc

Index: src/x64/full-codegen-x64.cc
===================================================================
--- src/x64/full-codegen-x64.cc	(revision 9277)
+++ src/x64/full-codegen-x64.cc	(working copy)
@@ -147,6 +147,11 @@
     __ bind(&ok);
   }
 
+  // Open a frame scope to indicate that there is a frame on the stack.  The
+  // MANUAL indicates that the scope shouldn't actually generate code to set up
+  // the frame (that is done below).
+  FrameScope frame_scope(masm_, StackFrame::MANUAL);
+
   __ push(rbp);  // Caller's frame pointer.
   __ movq(rbp, rsp);
   __ push(rsi);  // Callee's context.