Reapply "Do not directly load smi constants larger than a 16 bit..."

runtime/vm/assembler_x64.h

Index: runtime/vm/assembler_x64.h
diff --git a/runtime/vm/assembler_x64.h b/runtime/vm/assembler_x64.h
index 8464b06b17cc27aa161a1bacef905e2c0eb43096..f8c1307c9caa4ecc596feb51d588503aaada8752 100644
--- a/runtime/vm/assembler_x64.h
+++ b/runtime/vm/assembler_x64.h
@@ -13,6 +13,7 @@
 #include "platform/utils.h"
 #include "vm/constants_x64.h"
 #include "vm/hash_map.h"
+#include "vm/object.h"
 
 namespace dart {
 
@@ -847,6 +848,11 @@ class Assembler : public ValueObject {
 
   static const char* FpuRegisterName(FpuRegister reg);
 
+  // On some other platforms, we draw a distinction between safe and unsafe
+  // smis.
+  static bool IsSafe(const Object& object) { return true; }
+  static bool IsSafeSmi(const Object& object) { return object.IsSmi(); }
+
  private:
   AssemblerBuffer buffer_;