Don't issue texture barriers for RT's with separate storage

BUG=skia:

Review URL: https://codereview.chromium.org/1137663004
diff --git a/src/gpu/GrCommandBuilder.cpp b/src/gpu/GrCommandBuilder.cpp
index 2ff59bc..106e781 100644
--- a/src/gpu/GrCommandBuilder.cpp
+++ b/src/gpu/GrCommandBuilder.cpp
@@ -82,7 +82,7 @@
         return NULL;
     }
 
-    XferBarrier* xb = GrNEW_APPEND_TO_RECORDER(*this->cmdBuffer(), XferBarrier, ());
+    XferBarrier* xb = GrNEW_APPEND_TO_RECORDER(*this->cmdBuffer(), XferBarrier, (rt));
     xb->fBarrierType = barrierType;
     return xb;
 }