color: Clarify default behaviors

media/filters/vpx_video_decoder.cc

Index: media/filters/vpx_video_decoder.cc
diff --git a/media/filters/vpx_video_decoder.cc b/media/filters/vpx_video_decoder.cc
index 07b1bed0b5cb0ae9807b3cfb54061200cf95195b..bce019226fdb5d8669122e1a308ac1289a04e146 100644
--- a/media/filters/vpx_video_decoder.cc
+++ b/media/filters/vpx_video_decoder.cc
@@ -604,11 +604,9 @@ bool VpxVideoDecoder::VpxDecode(const scoped_refptr<DecoderBuffer>& buffer,
     // bitstream data below.
     (*video_frame)->set_color_space(config_.color_space_info());
   } else {
-    gfx::ColorSpace::PrimaryID primaries =
-        gfx::ColorSpace::PrimaryID::UNSPECIFIED;
-    gfx::ColorSpace::TransferID transfer =
-        gfx::ColorSpace::TransferID::UNSPECIFIED;
-    gfx::ColorSpace::MatrixID matrix = gfx::ColorSpace::MatrixID::UNSPECIFIED;
+    gfx::ColorSpace::PrimaryID primaries = gfx::ColorSpace::PrimaryID::BT709;
+    gfx::ColorSpace::TransferID transfer = gfx::ColorSpace::TransferID::BT709;
+    gfx::ColorSpace::MatrixID matrix = gfx::ColorSpace::MatrixID::BT709;
     gfx::ColorSpace::RangeID range = vpx_image->range == VPX_CR_FULL_RANGE
                                          ? gfx::ColorSpace::RangeID::FULL
                                          : gfx::ColorSpace::RangeID::LIMITED;
@@ -651,11 +649,8 @@ bool VpxVideoDecoder::VpxDecode(const scoped_refptr<DecoderBuffer>& buffer,
         break;
     }
 

[ccameron, 2017/02/15 21:57:23]

This is a behavior change.

The decision of how to treat unspecified color should be made here, and not
tossed further down the pipeline, where information about where the unspecified
values came from has been lost.

-    if (primaries != gfx::ColorSpace::PrimaryID::UNSPECIFIED) {
-      (*video_frame)
-          ->set_color_space(
-              gfx::ColorSpace(primaries, transfer, matrix, range));
-    }
+    (*video_frame)
+        ->set_color_space(gfx::ColorSpace(primaries, transfer, matrix, range));
   }
 
   return true;