Fix gpu mipmap support on ChromeOS

gpu/command_buffer/service/texture_manager.cc

Index: gpu/command_buffer/service/texture_manager.cc
diff --git a/gpu/command_buffer/service/texture_manager.cc b/gpu/command_buffer/service/texture_manager.cc
index f6a75dd40e91325cd5bc88ee00c8f5b83fb822d3..8b22a77573a6355ba6f7cc0f30f637423c10756c 100644
--- a/gpu/command_buffer/service/texture_manager.cc
+++ b/gpu/command_buffer/service/texture_manager.cc
@@ -2882,7 +2882,14 @@ GLenum TextureManager::AdjustTexInternalFormat(
         GetCompatibilitySwizzle(format);
     if (swizzle)
       return swizzle->dest_format;
+
+    // Compatibility format substitutions that do not require swizzling
+    if (format == GL_BGRA_EXT)
+      return GL_RGBA;
+    if (format == GL_BGRA8_EXT)
+      return GL_RGBA8;

[piman, 2016/07/19 20:32:30]

This transformation should already happen at a lower level - see
GetTexInternalFormat/GetInternalFormat in ui/gl/gl_gl_api_implementation.cc.
What is it that requires this?

(in the future, I want to coalesce all this, see also crbug.com/628064, but for
now I'd prefer keeping these things in a single place, otherwise it gets super
confusing).

[Justin Novosad, 2016/07/19 21:45:25]

Thanks for pointing this out. I did a bit of investigation and I found that on
ChromeOS (ozone) the gl implementation gets set to kGLImplementationEGLGLES2,
which prevents the substitution from happening in GetInternalFormat

I don't know enough about the ChromeOS config, but could this be a
misrepresentation of the Mesa driver?  make an exception for Mesa?

[piman, 2016/07/19 21:56:08]

Ah, Ozone indeed does use the ES backend of Mesa. This substitution would be
illegal on ES2 + GL_EXT_texture_format_BGRA8888.

If Mesa expects RGBA instead of BGRA as the internal format, it sounds like a
driver bug? If so we would need to add a workaround entry, and only do this
transformation if the workaround is active.

   }
+
   return format;
 }