Implement Mojo IPC for media::HDRMetadata

media/base/hdr_metadata.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MEDIA_BASE_HDR_METADATA_H_
 #define MEDIA_BASE_HDR_METADATA_H_
 
 #include "media/base/media_export.h"
 
 namespace media {
@@ skipping 24 matching lines @@
             (white_point_chromaticity_x == rhs.white_point_chromaticity_x) &&
             (white_point_chromaticity_y == rhs.white_point_chromaticity_y) &&
             (luminance_max == rhs.luminance_max) &&
             (luminance_min == rhs.luminance_min));
   }
 };
 
 // HDR metadata common for HDR10 and WebM/VP9-based HDR formats.
 struct MEDIA_EXPORT HDRMetadata {
   MasteringMetadata mastering_metadata;
+  // Max content light level (CLL), i.e. maximum brightness level present in the
+  // stream), in nits.
   unsigned max_cll = 0;
+  // Max frame-average light level (FALL), i.e. maximum average brightness of
+  // the brightest frame in the stream), in nits.
   unsigned max_fall = 0;

[xhwang, 2017/04/07 16:46:05]

Thank you for adding the comments!

Per the style guide:
https://google.github.io/styleguide/cppguide.html#General_Naming_Rules

"Names should be descriptive; avoid abbreviation... Do not use abbreviations
that are ambiguous or unfamiliar to readers outside your project."

By doing a Google search [1], I don't feel "content light level" is a well known
concept (with 8530 search results), let alone the abbreviated form.

[1]
https://www.google.com/search?q=content+light+level&oq=content+light+level&aq...

But feel free to land the current CL since these are existing code. And we can
fix this later.

 
   HDRMetadata();
   HDRMetadata(const HDRMetadata& rhs);
 
   bool operator==(const HDRMetadata& rhs) const {
     return ((max_cll == rhs.max_cll) && (max_fall == rhs.max_fall) &&
             (mastering_metadata == rhs.mastering_metadata));
   }
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_HDR_METADATA_H_