Make array allocation stub shared between isolates.

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 d7e05f162df4121bf688200a8a7f46d9c7e958ca..12ad8c41042a6807b0ef5ec115023c28d251c97b 100644
--- a/runtime/vm/gc_marker.cc
+++ b/runtime/vm/gc_marker.cc
@@ -317,10 +317,9 @@ class MarkingVisitor : public ObjectPointerVisitor {
         // If the code wasn't strongly visited through other references
         // after skipping the function's code pointer, then we disconnect the
         // code from the function.
-        StubCode* stub_code = isolate()->stub_code();
         func->StorePointer(
             &(func->ptr()->instructions_),
-            stub_code->LazyCompile_entry()->code()->ptr()->instructions_);
+            StubCode::LazyCompile_entry()->code()->ptr()->instructions_);
         if (FLAG_log_code_drop) {
           // NOTE: This code runs while GC is in progress and runs within
           // a NoHandleScope block. Hence it is not okay to use a regular Zone