Replace deprecated base::NonThreadSafe in content/child/fileapi in favor of SequenceChecker.

content/child/fileapi/webfilesystem_impl.h

Index: content/child/fileapi/webfilesystem_impl.h
diff --git a/content/child/fileapi/webfilesystem_impl.h b/content/child/fileapi/webfilesystem_impl.h
index bef376f1a80c510ceb7506367487520c7b8e2f2c..4efe2f9463a0b5da06b0b431a342a2da0fd205a1 100644
--- a/content/child/fileapi/webfilesystem_impl.h
+++ b/content/child/fileapi/webfilesystem_impl.h
@@ -10,7 +10,7 @@
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
-#include "base/threading/non_thread_safe.h"
+#include "base/sequence_checker.h"
 #include "content/public/child/worker_thread.h"
 #include "third_party/WebKit/public/platform/WebFileSystem.h"
 
@@ -26,8 +26,7 @@ class WebFileWriterClient;
 namespace content {
 
 class WebFileSystemImpl : public blink::WebFileSystem,
-                          public WorkerThread::Observer,
-                          public base::NonThreadSafe {
+                          public WorkerThread::Observer {
  public:
   class WaitableCallbackResults;
 
@@ -107,6 +106,8 @@ class WebFileSystemImpl : public blink::WebFileSystem,
   int next_callbacks_id_;
   WaitableCallbackResultsMap waitable_results_;
 
+  SEQUENCE_CHECKER(sequence_checker_);
+
   DISALLOW_COPY_AND_ASSIGN(WebFileSystemImpl);
 };