Add x64 implementation test support for assembler and code generator.

src/x64/macro-assembler-x64.cc

Index: src/x64/macro-assembler-x64.cc
===================================================================
--- src/x64/macro-assembler-x64.cc	(revision 2140)
+++ src/x64/macro-assembler-x64.cc	(working copy)
@@ -59,6 +59,21 @@
 }
 
 
+void MacroAssembler::ConstructAndTestJSFunction() {
+  const int initial_buffer_size = 4 * KB;
+  char* buffer = new char[initial_buffer_size];
+  MacroAssembler masm(buffer, initial_buffer_size);
+#define __ ACCESS_MASM((&masm))
+  // Construct a simple JSfunction here, using Assembler and MacroAssembler
+  // commands.
+  __ int3();
+#undef __
+  CodeDesc desc;
+  masm.GetCode(&desc);
+  // TODO(X64): Create the function object and call it.
+}
+
+
 void MacroAssembler::Abort(const char* msg) {
   // We want to pass the msg string like a smi to avoid GC
   // problems, however msg is not guaranteed to be aligned