Use access_mode in argument in a constructor of IsolateHolder.

gin::IsolateHolder has 3 types of constructors, and one of them
igored an argument.
This CL makes it to use |access_mode| in the argument.

BUG=None

Review-Url: https://codereview.chromium.org/2709473002
Cr-Commit-Position: refs/heads/master@{#451583}
diff --git a/gin/isolate_holder.cc b/gin/isolate_holder.cc
index 637b488..caea27e 100644
--- a/gin/isolate_holder.cc
+++ b/gin/isolate_holder.cc
@@ -34,9 +34,7 @@
 IsolateHolder::IsolateHolder(
     scoped_refptr<base::SingleThreadTaskRunner> task_runner,
     AccessMode access_mode)
-    : IsolateHolder(std::move(task_runner),
-                    AccessMode::kSingleThread,
-                    kAllowAtomicsWait) {}
+    : IsolateHolder(std::move(task_runner), access_mode, kAllowAtomicsWait) {}
 
 IsolateHolder::IsolateHolder(
     scoped_refptr<base::SingleThreadTaskRunner> task_runner,