Use highp for distance field texture coordinates.

src/gpu/GrDistanceFieldTextContext.cpp

Index: src/gpu/GrDistanceFieldTextContext.cpp
diff --git a/src/gpu/GrDistanceFieldTextContext.cpp b/src/gpu/GrDistanceFieldTextContext.cpp
index 425c56c892ed2ccf50c8b1ea3781e18437858d25..820223ddc49d1d9084db580b56c201a508d880be 100755
--- a/src/gpu/GrDistanceFieldTextContext.cpp
+++ b/src/gpu/GrDistanceFieldTextContext.cpp
@@ -33,9 +33,9 @@ SK_CONF_DECLARE(bool, c_DumpFontCache, "gpu.dumpFontCache", false,
 
 static const int kSmallDFFontSize = 32;
 static const int kSmallDFFontLimit = 32;
-static const int kMediumDFFontSize = 78;
-static const int kMediumDFFontLimit = 78;
-static const int kLargeDFFontSize = 192;
+static const int kMediumDFFontSize = 64;
+static const int kMediumDFFontLimit = 64;
+static const int kLargeDFFontSize = 128;
 
 static const int kVerticesPerGlyph = 4;
 static const int kIndicesPerGlyph = 6;