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..eb474abd5c5be6aa89a7a761de0065b3ed90980f 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::INVALID;
+    gfx::ColorSpace::TransferID transfer = gfx::ColorSpace::TransferID::INVALID;
+    gfx::ColorSpace::MatrixID matrix = gfx::ColorSpace::MatrixID::INVALID;
     gfx::ColorSpace::RangeID range = vpx_image->range == VPX_CR_FULL_RANGE
                                          ? gfx::ColorSpace::RangeID::FULL
                                          : gfx::ColorSpace::RangeID::LIMITED;
@@ -651,7 +649,7 @@ bool VpxVideoDecoder::VpxDecode(const scoped_refptr<DecoderBuffer>& buffer,
         break;
     }
 
-    if (primaries != gfx::ColorSpace::PrimaryID::UNSPECIFIED) {
+    if (primaries != gfx::ColorSpace::PrimaryID::INVALID) {
       (*video_frame)
           ->set_color_space(
               gfx::ColorSpace(primaries, transfer, matrix, range));