Reland "Add Y4mFileReader"

This is a reland of 404be7f302358e6be16aadeba8bc8f8aba348c0f
It adds support for reading .yuv files as well to not break anything.

Original change's description:
> Add Y4mFileReader
>
> Encapsulate logic for reading .y4m video files in a single class. We
> currently have spread out logic for opening .y4m files with partial
> parsing. This CL consolidates this logic into a single class with a well
> defined interface.
>
> Change-Id: Id61673b3c95a0053b30e95b4cf382e1c6b05fc30
> Bug: webrtc:9642
> Reviewed-on: https://webrtc-review.googlesource.com/94772
> Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
> Reviewed-by: Paulina Hensman <phensman@webrtc.org>
> Commit-Queue: Magnus Jedvert <magjed@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#24398}

TBR=phensman,phoglund

Bug: webrtc:9642
Change-Id: Idecc5ec5da767221a5f5b439989f4fe07e3b3615
Reviewed-on: https://webrtc-review.googlesource.com/97983
Commit-Queue: Magnus Jedvert <magjed@webrtc.org>
Reviewed-by: Magnus Jedvert <magjed@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24571}

rtc_tools/video_file_reader.h

@@ -0,0 +1,80 @@
+/*
+ *  Copyright (c) 2018 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+#ifndef RTC_TOOLS_VIDEO_FILE_READER_H_
+#define RTC_TOOLS_VIDEO_FILE_READER_H_
+
+#include <cstdio>
+#include <iterator>
+#include <string>
+#include <vector>
+
+#include "api/video/video_frame.h"
+#include "rtc_base/refcount.h"
+
+namespace webrtc {
+namespace test {
+
+// Iterable class representing a sequence of I420 buffers. This class is not
+// thread safe because it is expected to be backed by a file.
+class Video : public rtc::RefCountInterface {
+ public:
+  class Iterator {
+   public:
+    typedef int value_type;
+    typedef std::ptrdiff_t difference_type;
+    typedef int* pointer;
+    typedef int& reference;
+    typedef std::input_iterator_tag iterator_category;
+
+    Iterator(const rtc::scoped_refptr<const Video>& video, size_t index);
+    Iterator(const Iterator& other);
+    Iterator(Iterator&& other);
+    Iterator& operator=(Iterator&&);
+    Iterator& operator=(const Iterator&);
+    ~Iterator();
+
+    rtc::scoped_refptr<I420BufferInterface> operator*() const;
+    bool operator==(const Iterator& other) const;
+    bool operator!=(const Iterator& other) const;
+
+    Iterator operator++(int);
+    Iterator& operator++();
+
+   private:
+    rtc::scoped_refptr<const Video> video_;
+    size_t index_;
+  };
+
+  Iterator begin() const;
+  Iterator end() const;
+
+  virtual int width() const = 0;
+  virtual int height() const = 0;
+  virtual size_t number_of_frames() const = 0;
+  virtual rtc::scoped_refptr<I420BufferInterface> GetFrame(
+      size_t index) const = 0;
+};
+
+rtc::scoped_refptr<Video> OpenY4mFile(const std::string& file_name);
+
+rtc::scoped_refptr<Video> OpenYuvFile(const std::string& file_name,
+                                      int width,
+                                      int height);
+
+// This is a helper function for the two functions above. It reads the file
+// extension to determine whether it is a .yuv or a .y4m file.
+rtc::scoped_refptr<Video> OpenYuvOrY4mFile(const std::string& file_name,
+                                           int width,
+                                           int height);
+
+}  // namespace test
+}  // namespace webrtc
+
+#endif  // RTC_TOOLS_VIDEO_FILE_READER_H_