Make GrGpu::deleteTestingOnlyBackendTexture() take const GrBackendTexture&

Change-Id: Ibd00d0dc6d8c73628f26851e102defdbafab149b
Reviewed-on: https://skia-review.googlesource.com/113164
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
diff --git a/tests/WritePixelsTest.cpp b/tests/WritePixelsTest.cpp
index adab3a0..f00d092 100644
--- a/tests/WritePixelsTest.cpp
+++ b/tests/WritePixelsTest.cpp
@@ -431,7 +431,7 @@
         if (surface) {
             test_write_pixels(reporter, surface.get());
         }
-        gpu->deleteTestingOnlyBackendTexture(&backendTex);
+        gpu->deleteTestingOnlyBackendTexture(backendTex);
     }
 }