Reland of Make a single GrSingleOwner in GrContext

include/gpu/GrContext.h

Index: include/gpu/GrContext.h
diff --git a/include/gpu/GrContext.h b/include/gpu/GrContext.h
index 39477e0db81fbdc0875aec82f4220664336be11f..baf99789c0b8f965ed5da23c9d617243c60e99ab 100644
--- a/include/gpu/GrContext.h
+++ b/include/gpu/GrContext.h
@@ -392,7 +392,9 @@
     SkMutex                         fTestPMConversionsMutex;
 
     // In debug builds we guard against improper thread handling
-    SkDEBUGCODE(mutable GrSingleOwner fSingleOwner;)
+    // This guard is passed to the GrDrawingManager and, from there to all the
+    // GrDrawContexts.  It is also passed to the GrTextureProvider and SkGpuDevice.
+    mutable GrSingleOwner fSingleOwner;
 
     struct CleanUpData {
         PFCleanUpFunc fFunc;