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/src/gpu/glsl/GrGLSLFragmentShaderBuilder.cpp b/src/gpu/glsl/GrGLSLFragmentShaderBuilder.cpp
index 4fd886b..6c0528e 100644
--- a/src/gpu/glsl/GrGLSLFragmentShaderBuilder.cpp
+++ b/src/gpu/glsl/GrGLSLFragmentShaderBuilder.cpp
@@ -300,7 +300,7 @@
 void GrGLSLFragmentShaderBuilder::defineSampleOffsetArray(const char* name, const SkMatrix& m) {
     SkASSERT(fProgramBuilder->caps()->sampleLocationsSupport());
     const GrPipeline& pipeline = fProgramBuilder->pipeline();
-    const GrRenderTargetPriv& rtp = pipeline.getRenderTarget()->renderTargetPriv();
+    const GrRenderTargetPriv& rtp = pipeline.renderTarget()->renderTargetPriv();
     const GrGpu::MultisampleSpecs& specs = rtp.getMultisampleSpecs(pipeline);
     SkSTArray<16, SkPoint, true> offsets;
     offsets.push_back_n(specs.fEffectiveSampleCnt);