Use presence of a content key as non-scratch indicator

BUG=skia:2889

Committed: https://skia.googlesource.com/skia/+/9eefe0851eeaa8ded05b4774ebcb38ed201d5dbf

Review URL: https://codereview.chromium.org/639873002
diff --git a/src/gpu/GrResourceCache2.cpp b/src/gpu/GrResourceCache2.cpp
index 85e66a7..5144c59 100644
--- a/src/gpu/GrResourceCache2.cpp
+++ b/src/gpu/GrResourceCache2.cpp
@@ -67,15 +67,15 @@
             // either by drawing code or for pending io operations.
             // This will be removed when flush no longer creates resources.
             return resource->reffedOnlyByCache() && !resource->internalHasPendingIO() &&
-                   GrGpuResource::kYes_IsScratch == resource->fIsScratch;
+                   resource->isScratch();
         } else {
             // Because duties are currently shared between GrResourceCache and GrResourceCache2, the
             // current interpretation of this rule is that only GrResourceCache has a ref but that
             // it has been marked as a scratch resource.
-            return resource->reffedOnlyByCache() &&
-                GrGpuResource::kYes_IsScratch == resource->fIsScratch;
+            return resource->reffedOnlyByCache() && resource->isScratch();
         }
     }
+
 private:
     bool fFlushing;
 };