Let text contexts fall back directly to paths

BUG=skia:

Review URL: https://codereview.chromium.org/1015173002
diff --git a/src/gpu/SkGpuDevice.h b/src/gpu/SkGpuDevice.h
index af6dd0b..be7857a 100644
--- a/src/gpu/SkGpuDevice.h
+++ b/src/gpu/SkGpuDevice.h
@@ -210,6 +210,7 @@
     static GrRenderTarget* CreateRenderTarget(GrContext*, SkSurface::Budgeted, const SkImageInfo&,
                                               int sampleCount);
 
+    friend class GrTextContext;
     typedef SkBaseDevice INHERITED;
 };