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/src/gpu/GrDistanceFieldTextContext.cpp b/src/gpu/GrDistanceFieldTextContext.cpp
index 1976cf1..58c8121 100755
--- a/src/gpu/GrDistanceFieldTextContext.cpp
+++ b/src/gpu/GrDistanceFieldTextContext.cpp
@@ -64,7 +64,7 @@
                                                        const SkDeviceProperties& properties,
                                                        bool enable)
                                                     : GrTextContext(context, properties) {
-#if SK_FORCE_DISTANCEFIELD_FONTS
+#if SK_FORCE_DISTANCE_FIELD_TEXT
     fEnableDFRendering = true;
 #else
     fEnableDFRendering = enable;