Implement Mojo IPC for media::HDRMetadata

media/base/hdr_metadata.h

Index: media/base/hdr_metadata.h
diff --git a/media/base/hdr_metadata.h b/media/base/hdr_metadata.h
index 2808e1738927720387885868c60cf8d41735f387..78a17756ca8665f889e46ef73bd635300eea79a7 100644
--- a/media/base/hdr_metadata.h
+++ b/media/base/hdr_metadata.h
@@ -42,7 +42,11 @@ struct MEDIA_EXPORT MasteringMetadata {
 // 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();