Get rid of deprecated methods accessing mutator_thread_ instead of current thread

runtime/vm/object_graph_test.cc

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "platform/assert.h"
 #include "vm/object_graph.h"
 #include "vm/unit_test.h"
 
 namespace dart {
 
@@ skipping 47 matching lines @@
   intptr_t c_size = c.raw()->Size();
   intptr_t d_size = d.raw()->Size();
   {
     // No more allocation; raw pointers ahead.
     NoSafepointScope no_safepoint_scope;
     RawObject* b_raw = b.raw();
     // Clear handles to cut unintended retained paths.
     b = Array::null();
     c = Array::null();
     d = Array::null();
-    ObjectGraph graph(isolate);
+    ObjectGraph graph(thread);
     {
       // Compare count and size when 'b' is/isn't skipped.
       CounterVisitor with(Object::null(), Object::null());
       graph.IterateObjectsFrom(a, &with);
       CounterVisitor without(b_raw, a.raw());
       graph.IterateObjectsFrom(a, &without);
       // Only 'b' and 'c' were cut off.
       EXPECT_EQ(2, with.count() - without.count());
       EXPECT_EQ(b_size + c_size,
                 with.size() - without.size());
@@ skipping 10 matching lines @@
                 with.size() - without.size());
     }
     EXPECT_EQ(a_size + b_size + c_size + d_size,
               graph.SizeRetainedByInstance(a));
   }
   {
     // Get hold of c again.
     b ^= a.At(10);
     c ^= b.At(0);
     b = Array::null();
-    ObjectGraph graph(isolate);
+    ObjectGraph graph(thread);
     // A retaining path should end like this: c <- b <- a <- ...
     {
       HANDLESCOPE(thread);
       // Test null, empty, and length 1 array.
       intptr_t null_length = graph.RetainingPath(&c, Object::null_array());
       intptr_t empty_length = graph.RetainingPath(&c, Object::empty_array());
       Array& path = Array::Handle(Array::New(1, Heap::kNew));
       intptr_t one_length = graph.RetainingPath(&c, path);
       EXPECT_EQ(null_length, empty_length);
       EXPECT_EQ(null_length, one_length);
@@ skipping 22 matching lines @@
       Array& expected_a = Array::Handle();
       expected_a ^= path.At(4);
       EXPECT(expected_c.raw() == c.raw());
       EXPECT(expected_b.raw() == a.At(10));
       EXPECT(expected_a.raw() == a.raw());
     }
   }
 }
 
 }  // namespace dart