Get gpudft support working in dm, gm, nanobench and bench_pictures

Adds a new config to test distance field text.
Clean up some flags and #defines to read "distance field text",
not "distance field fonts" to be consistent with Chromium

NOTREECHECKS=true

Committed: https://skia.googlesource.com/skia/+/06ba179838ba4fe187cf290750aeeb4a02a2960b

Review URL: https://codereview.chromium.org/699453005
diff --git a/dm/DMGpuGMTask.h b/dm/DMGpuGMTask.h
index 23f3a45..553436d 100644
--- a/dm/DMGpuGMTask.h
+++ b/dm/DMGpuGMTask.h
@@ -22,7 +22,8 @@
               skiagm::GMRegistry::Factory,
               GrContextFactory::GLContextType,
               GrGLStandard gpuAPI,
-              int sampleCount);
+              int sampleCount,
+              bool useDFText);
 
     virtual void draw(GrContextFactory*) SK_OVERRIDE;
     virtual bool shouldSkip() const SK_OVERRIDE;
@@ -34,6 +35,7 @@
     const GrContextFactory::GLContextType fContextType;
     GrGLStandard fGpuAPI;
     const int fSampleCount;
+    const bool fUseDFText;
 };
 
 }  // namespace DM