Change Config to a struct and rename it's members.

BUG=angle:658

Change-Id: I18dab915730fc28815db8080b3614da821f9c8b1
Reviewed-on: https://chromium-review.googlesource.com/239901
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>
diff --git a/src/libANGLE/Texture.cpp b/src/libANGLE/Texture.cpp
index b268fd8..9dde07e 100644
--- a/src/libANGLE/Texture.cpp
+++ b/src/libANGLE/Texture.cpp
@@ -416,7 +416,7 @@
     // Set the image info to the size and format of the surface
     ASSERT(mTarget == GL_TEXTURE_2D);
     Extents size(surface->getWidth(), surface->getHeight(), 1);
-    ImageDesc desc(size, surface->getConfig()->mRenderTargetFormat);
+    ImageDesc desc(size, surface->getConfig()->renderTargetFormat);
     setImageDesc(ImageIndex::MakeGeneric(mTarget, 0), desc);
 }