Shrink AOT snapshot size and memory usage.

runtime/vm/gc_marker.cc

Index: runtime/vm/gc_marker.cc
diff --git a/runtime/vm/gc_marker.cc b/runtime/vm/gc_marker.cc
index 7ea64d6168fec374d69eb9f804f024c701f2a563..ed6d4da5eb284742f5595224b43e836661a8fd9a 100644
--- a/runtime/vm/gc_marker.cc
+++ b/runtime/vm/gc_marker.cc
@@ -30,6 +30,9 @@ class SkippedCodeFunctions : public ZoneAllocated {
   }
 
   void DetachCode() {
+#if defined(DART_PRECOMPILED_RUNTIME)
+    UNREACHABLE();
+#else
     intptr_t unoptimized_code_count = 0;
     intptr_t current_code_count = 0;
     for (int i = 0; i < skipped_code_functions_.length(); i++) {
@@ -76,6 +79,7 @@ class SkippedCodeFunctions : public ZoneAllocated {
     }
     // Clean up.
     skipped_code_functions_.Clear();
+#endif  // !DART_PRECOMPILED_RUNTIME
   }
 
  private: