Add GrBackendTexture & GrBackendRenderTarget access methods to GrTexture and GrRenderTarget

Change-Id: I627fcc2cab1d04169f49e33a6c17e161e9a9772a
Reviewed-on: https://skia-review.googlesource.com/84621
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
diff --git a/tests/ImageFilterCacheTest.cpp b/tests/ImageFilterCacheTest.cpp
index 449b252..bcd4511 100644
--- a/tests/ImageFilterCacheTest.cpp
+++ b/tests/ImageFilterCacheTest.cpp
@@ -215,12 +215,8 @@
     }
     GrTexture* tex = srcProxy->priv().peekTexture();
 
-    GrBackendTexture backendTex = GrTest::CreateBackendTexture(context->contextPriv().getBackend(),
-                                                               kFullSize,
-                                                               kFullSize,
-                                                               kRGBA_8888_GrPixelConfig,
-                                                               GrMipMapped::kNo,
-                                                               tex->getTextureHandle());
+    GrBackendTexture backendTex = tex->getBackendTexture();
+
     GrSurfaceOrigin texOrigin = kTopLeft_GrSurfaceOrigin;
     sk_sp<SkImage> srcImage(SkImage::MakeFromTexture(context,
                                                      backendTex,