Merge all gl::Texture* classes.

The validation for sampler completeness had a lot of duplicated code.
The special cases have been merged into the base class by checking mTarget.

BUG=angle:681

Change-Id: I11d94c1432f8fc70a1edaaf8228bbc43c3c8fff3
Reviewed-on: https://chromium-review.googlesource.com/236932
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>
diff --git a/src/libANGLE/FramebufferAttachment.cpp b/src/libANGLE/FramebufferAttachment.cpp
index d09a78a..4b2552a 100644
--- a/src/libANGLE/FramebufferAttachment.cpp
+++ b/src/libANGLE/FramebufferAttachment.cpp
@@ -123,7 +123,7 @@
 
 GLenum TextureAttachment::cubeMapFace() const
 {
-    return IsCubemapTextureTarget(mIndex.type) ? mIndex.type : GL_NONE;
+    return IsCubeMapTextureTarget(mIndex.type) ? mIndex.type : GL_NONE;
 }
 
 GLint TextureAttachment::layer() const