color: Clarify default behaviors

cc/output/gl_renderer.cc

 // Copyright 2010 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.
 
 #include "cc/output/gl_renderer.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 2091 matching lines @@
         src_color_space = gfx::ColorSpace::CreateREC601();
         break;
       case YUVVideoDrawQuad::REC_709:
         src_color_space = gfx::ColorSpace::CreateREC709();
         break;
       case YUVVideoDrawQuad::JPEG:
         src_color_space = gfx::ColorSpace::CreateJpeg();
         break;
     }
   }
+  // Invalid or unspecified color spaces should be treated as REC709.
+  if (!src_color_space.IsValid())
+    src_color_space = gfx::ColorSpace::CreateREC709();
 
   ResourceProvider::ScopedSamplerGL y_plane_lock(
       resource_provider_, quad->y_plane_resource_id(), GL_TEXTURE1, GL_LINEAR);
   ResourceProvider::ScopedSamplerGL u_plane_lock(
       resource_provider_, quad->u_plane_resource_id(), GL_TEXTURE2, GL_LINEAR);
   DCHECK_EQ(y_plane_lock.target(), u_plane_lock.target());
   // TODO(jbauman): Use base::Optional when available.
   std::unique_ptr<ResourceProvider::ScopedSamplerGL> v_plane_lock;
 
   if (uv_texture_mode == UV_TEXTURE_MODE_U_V) {
@@ skipping 1405 matching lines @@
     return;
 
   // Report GPU overdraw as a percentage of |max_result|.
   TRACE_COUNTER1(
       TRACE_DISABLED_BY_DEFAULT("cc.debug.overdraw"), "GPU Overdraw",
       (std::accumulate(overdraw->begin(), overdraw->end(), 0) * 100) /
           max_result);
 }
 
 }  // namespace cc