Introduce enum class for texture type.

This represents the GL texture "target" but at the API-neutral level. It
will be needed here because proxy's that wrap imported texture's need to
know about sampling restrictions.

Change-Id: Ie811a6f6d04ba1b04faa6908422dca64e8e447c8
Reviewed-on: https://skia-review.googlesource.com/144304
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
diff --git a/src/gpu/ops/GrTextureOp.cpp b/src/gpu/ops/GrTextureOp.cpp
index ff01985..99ecdf8 100644
--- a/src/gpu/ops/GrTextureOp.cpp
+++ b/src/gpu/ops/GrTextureOp.cpp
@@ -953,7 +953,7 @@
                 return -1;
             }
             if (GrTexture* tex = thatProxies[j]->priv().peekTexture()) {
-                if (tex->texturePriv().samplerType() != kTexture2DSampler_GrSLType) {
+                if (tex->texturePriv().textureType() != GrTextureType::k2D) {
                     return -1;
                 }
             }