Add IsMutatorThread to the Thread class and use it instead of MutatorThreadIsCurrentThread

runtime/vm/compiler.cc

 // Copyright (c) 2012, 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 "vm/compiler.h"
 
 #include "vm/assembler.h"
 
 #include "vm/ast_printer.h"
 #include "vm/block_scheduler.h"
@@ skipping 1147 matching lines @@
 RawError* Compiler::CompileOptimizedFunction(Thread* thread,
                                              const Function& function,
                                              intptr_t osr_id) {
   VMTagScope tagScope(thread, VMTag::kCompileOptimizedTagId);
   TIMELINE_FUNCTION_COMPILATION_DURATION(thread,
                                          "OptimizedFunction", function);
 
   // Optimization must happen in non-mutator/Dart thread if background
   // compilation is on. OSR compilation still occurs in the main thread.
   ASSERT((osr_id != Thread::kNoDeoptId) || !FLAG_background_compilation ||
-         !thread->isolate()->MutatorThreadIsCurrentThread());
+         !thread->IsMutatorThread());
   CompilationPipeline* pipeline =
       CompilationPipeline::New(thread->zone(), function);
   return CompileFunctionHelper(pipeline, function, true, osr_id);
 }
 
 
 // This is only used from unit tests.
 RawError* Compiler::CompileParsedFunction(
     ParsedFunction* parsed_function) {
   LongJumpScope jump;
@@ skipping 404 matching lines @@
           thread->zone(), GrowableObjectArray::New()));
       start_task = true;
     }
   }
   if (start_task) {
     Dart::thread_pool()->Run(isolate->background_compiler());
   }
 }
 
 }  // namespace dart