VM: Link native calls lazily.

runtime/vm/code_patcher_arm64.cc

Index: runtime/vm/code_patcher_arm64.cc
diff --git a/runtime/vm/code_patcher_arm64.cc b/runtime/vm/code_patcher_arm64.cc
index 7b0afef646b834eb8ff43dd34959aae7b74fb7bf..3e10b5a35512076d78095afef2f5abf68c05c427 100644
--- a/runtime/vm/code_patcher_arm64.cc
+++ b/runtime/vm/code_patcher_arm64.cc
@@ -118,6 +118,27 @@ RawFunction* CodePatcher::GetUnoptimizedStaticCallAt(
 }
 
 
+void CodePatcher::PatchNativeCallAt(uword return_address,
+                                    const Code& code,
+                                    NativeFunction target,
+                                    const Code& trampoline) {
+  ASSERT(code.ContainsInstructionAt(return_address));
+  NativeCallPattern call(return_address, code);
+  call.set_target(trampoline.EntryPoint());
+  call.set_native_function(target);
+}
+
+
+uword CodePatcher::GetNativeCallAt(uword return_address,
+                                   const Code& code,
+                                   NativeFunction* target) {
+  ASSERT(code.ContainsInstructionAt(return_address));
+  NativeCallPattern call(return_address, code);
+  *target = call.native_function();
+  return call.target();
+}
+
+
 // This class pattern matches on a load from the object pool.  Loading on
 // ARM64 is complicated because it can take more than one form.  We
 // match backwards from the end of the sequence so we can reuse the code for