Fix data race when concurrent compilation is aborted due to dependency change.

src/compiler.h

Index: src/compiler.h
diff --git a/src/compiler.h b/src/compiler.h
index e9176d322d950b0b3c0d9c8ef0afd328a13561ed..4564b9004f7a333026a45520cc0f4fd8f88f91db 100644
--- a/src/compiler.h
+++ b/src/compiler.h
@@ -85,8 +85,7 @@ class CompilationInfo {
     kInliningEnabled = 1 << 17,
     kTypingEnabled = 1 << 18,
     kDisableFutureOptimization = 1 << 19,
-    kAbortedDueToDependency = 1 << 20,
-    kToplevel = 1 << 21
+    kToplevel = 1 << 20
   };
 
   CompilationInfo(Handle<JSFunction> closure, Zone* zone);
@@ -371,12 +370,12 @@ class CompilationInfo {
 
   void AbortDueToDependencyChange() {
     DCHECK(!OptimizingCompilerThread::IsOptimizerThread(isolate()));
-    SetFlag(kAbortedDueToDependency);
+    aborted_due_to_dependency_change_ = true;
   }
 
   bool HasAbortedDueToDependencyChange() const {
     DCHECK(!OptimizingCompilerThread::IsOptimizerThread(isolate()));
-    return GetFlag(kAbortedDueToDependency);
+    return aborted_due_to_dependency_change_;
   }
 
   bool HasSameOsrEntry(Handle<JSFunction> function, BailoutId osr_ast_id) {
@@ -515,6 +514,10 @@ class CompilationInfo {
   bool ast_value_factory_owned_;
   AstNode::IdGen ast_node_id_gen_;
 
+  // This flag is used by the main thread to track whether this compilation
+  // should be abandoned due to dependency change.
+  bool aborted_due_to_dependency_change_;
+
   DISALLOW_COPY_AND_ASSIGN(CompilationInfo);
 };