Add a use counter and histogram to FileReaderSync.

third_party/WebKit/Source/core/fileapi/FileReaderSync.h

Index: third_party/WebKit/Source/core/fileapi/FileReaderSync.h
diff --git a/third_party/WebKit/Source/core/fileapi/FileReaderSync.h b/third_party/WebKit/Source/core/fileapi/FileReaderSync.h
index b6dc4cac0137e489aef0244cd3d45955eb50f87b..14bc6e24c37cf9d818db0bec7e3efc0c76585568 100644
--- a/third_party/WebKit/Source/core/fileapi/FileReaderSync.h
+++ b/third_party/WebKit/Source/core/fileapi/FileReaderSync.h
@@ -49,7 +49,9 @@ class FileReaderSync final : public GarbageCollected<FileReaderSync>,
   DEFINE_WRAPPERTYPEINFO();
 
  public:
-  static FileReaderSync* create() { return new FileReaderSync(); }
+  static FileReaderSync* create(ExecutionContext* context) {
+    return new FileReaderSync(context);
+  }
 
   DOMArrayBuffer* readAsArrayBuffer(ScriptState*, Blob*, ExceptionState&);
   String readAsBinaryString(ScriptState*, Blob*, ExceptionState&);
@@ -65,7 +67,7 @@ class FileReaderSync final : public GarbageCollected<FileReaderSync>,
   DEFINE_INLINE_TRACE() {}
 
  private:
-  FileReaderSync();
+  explicit FileReaderSync(ExecutionContext*);
 
   void startLoading(ExecutionContext*,
                     FileReaderLoader&,