Don't enable CHROMIUM_ycbcr_420v_image when using mesa.

gpu/command_buffer/service/feature_info.cc

Index: gpu/command_buffer/service/feature_info.cc
diff --git a/gpu/command_buffer/service/feature_info.cc b/gpu/command_buffer/service/feature_info.cc
index d8edc1f7f5a5063d94bfea3c2650f8d3cd7cb58d..59970377549e361dc3fb30729089d5eac1bbcc96 100644
--- a/gpu/command_buffer/service/feature_info.cc
+++ b/gpu/command_buffer/service/feature_info.cc
@@ -1003,9 +1003,11 @@ void FeatureInfo::InitializeFeatures() {
   }
 
 #if defined(OS_MACOSX)
-  AddExtensionString("GL_CHROMIUM_iosurface");
-  AddExtensionString("GL_CHROMIUM_ycbcr_420v_image");
-  feature_flags_.chromium_image_ycbcr_420v = true;
+  if (gfx::GetGLImplementation() != gfx::kGLImplementationOSMesaGL) {
+    AddExtensionString("GL_CHROMIUM_iosurface");
+    AddExtensionString("GL_CHROMIUM_ycbcr_420v_image");
+    feature_flags_.chromium_image_ycbcr_420v = true;
+  }
 #endif
 
   if (extensions.Contains("GL_APPLE_ycbcr_422")) {