Move explicit backend object allocation API to GrContext

This initial portion of the API should be ready to go. Follow on CLs will add the other entry points.

Change-Id: Ia9c708046ba08b16f9a71558e2bf2c38279abe5d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/214680
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
diff --git a/tests/WritePixelsTest.cpp b/tests/WritePixelsTest.cpp
index 305630e..12d5f1b 100644
--- a/tests/WritePixelsTest.cpp
+++ b/tests/WritePixelsTest.cpp
@@ -455,7 +455,7 @@
                                           int sampleCnt) {
 
     for (auto& origin : { kTopLeft_GrSurfaceOrigin, kBottomLeft_GrSurfaceOrigin }) {
-        GrBackendTexture backendTex = context->priv().createBackendTexture(
+        GrBackendTexture backendTex = context->createBackendTexture(
                 DEV_W, DEV_H, kRGBA_8888_SkColorType, GrMipMapped::kNo, GrRenderable::kYes);
         if (!backendTex.isValid()) {
             continue;
@@ -467,7 +467,7 @@
             auto ii = SkImageInfo::MakeN32Premul(DEV_W, DEV_H);
             test_write_pixels(reporter, surface.get(), ii);
         }
-        context->priv().deleteBackendTexture(backendTex);
+        context->deleteBackendTexture(backendTex);
     }
 }