Add GrContext::defaultBackendFormat

TBR=bsalomon@google.com
Bug: 987392
Change-Id: I38ff649b25e78c0a02a8fd20f513db4be62abf43
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/229919
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
diff --git a/src/gpu/GrContextPriv.cpp b/src/gpu/GrContextPriv.cpp
index a949078..554fbda 100644
--- a/src/gpu/GrContextPriv.cpp
+++ b/src/gpu/GrContextPriv.cpp
@@ -419,8 +419,7 @@
         }
     }
 
-    GrBackendFormat backendFormat =
-            this->caps()->getBackendFormatFromColorType(SkColorTypeToGrColorType(colorType));
+    GrBackendFormat backendFormat = fContext->defaultBackendFormat(colorType, renderable);
     if (!backendFormat.isValid()) {
         return {};
     }