Rename GrDrawContext to GrRenderTargetContext

This is in preparation for GrTextureContext and GrSurfaceContext

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4030

Change-Id: Ie58c93052e68f3f1f5fe8d15d63760de274a6fbd
Reviewed-on: https://skia-review.googlesource.com/4030
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
diff --git a/gn/gpu.gni b/gn/gpu.gni
index 12e3b49..f300677 100644
--- a/gn/gpu.gni
+++ b/gn/gpu.gni
@@ -19,7 +19,6 @@
   "$_include/gpu/GrContextOptions.h",
   "$_include/gpu/GrContext.h",
   "$_include/gpu/GrCoordTransform.h",
-  "$_include/gpu/GrDrawContext.h",
   "$_include/gpu/GrFragmentProcessor.h",
   "$_include/gpu/GrGpuResource.h",
   "$_include/gpu/GrInvariantOutput.h",
@@ -29,6 +28,7 @@
   "$_include/gpu/GrProgramElement.h",
   "$_include/gpu/GrGpuResourceRef.h",
   "$_include/gpu/GrRenderTarget.h",
+  "$_include/gpu/GrRenderTargetContext.h",
   "$_include/gpu/GrResourceKey.h",
   "$_include/gpu/GrShaderVar.h",
   "$_include/gpu/GrSurface.h",
@@ -89,10 +89,6 @@
   "$_src/gpu/GrCoordTransform.cpp",
   "$_src/gpu/GrDefaultGeoProcFactory.cpp",
   "$_src/gpu/GrDefaultGeoProcFactory.h",
-  "$_src/gpu/GrDrawContext.cpp",
-  "$_src/gpu/GrDrawContextPriv.h",
-  "$_src/gpu/GrPathRenderingDrawContext.cpp",
-  "$_src/gpu/GrPathRenderingDrawContext.h",
   "$_src/gpu/GrDrawingManager.cpp",
   "$_src/gpu/GrDrawingManager.h",
   "$_src/gpu/GrFixedClip.cpp",
@@ -162,6 +158,10 @@
   "$_src/gpu/GrRenderTargetProxy.cpp",
   "$_src/gpu/GrReducedClip.cpp",
   "$_src/gpu/GrReducedClip.h",
+  "$_src/gpu/GrRenderTargetContext.cpp",
+  "$_src/gpu/GrRenderTargetContextPriv.h",
+  "$_src/gpu/GrPathRenderingRenderTargetContext.cpp",
+  "$_src/gpu/GrPathRenderingRenderTargetContext.h",
   "$_src/gpu/GrRenderTargetOpList.cpp",
   "$_src/gpu/GrRenderTargetOpList.h",
   "$_src/gpu/GrResourceCache.cpp",