Make GrPipeline hold a GrRenderTargetProxy (instead of a GrRenderTarget)

In a future world where GrSurface no longer has an origin it will be
useful for the GrPipeline to be holding the GrRenderTargetProxy (which will
still have an origin).

Change-Id: I743a8cc07b6b92f8116227fb77b7c37da43cde8a
Reviewed-on: https://skia-review.googlesource.com/26804
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
diff --git a/tests/GrSurfaceTest.cpp b/tests/GrSurfaceTest.cpp
index f1d6a26..71575c7 100644
--- a/tests/GrSurfaceTest.cpp
+++ b/tests/GrSurfaceTest.cpp
@@ -12,6 +12,7 @@
 #include "GrContext.h"
 #include "GrContextPriv.h"
 #include "GrGpu.h"
+#include "GrRenderTarget.h"
 #include "GrResourceProvider.h"
 #include "GrTest.h"
 #include "GrTexture.h"