"Port" (count >= 0) assertion in VirtualFrame::Drop to ia32 and x64.

Review URL: http://codereview.chromium.org/164251

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@2656 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/ia32/virtual-frame-ia32.cc

@@ -965,6 +965,7 @@ Result VirtualFrame::CallConstructor(int arg_count) {
 
 
 void VirtualFrame::Drop(int count) {
+  ASSERT(count >= 0);
   ASSERT(height() >= count);
   int num_virtual_elements = (element_count() - 1) - stack_pointer_;
 

src/x64/virtual-frame-x64.cc

@@ -206,6 +206,7 @@ void VirtualFrame::EmitPush(Handle<Object> value) {
 
 
 void VirtualFrame::Drop(int count) {
+  ASSERT(count >= 0);
   ASSERT(height() >= count);
   int num_virtual_elements = (element_count() - 1) - stack_pointer_;