use platform-independent font for gm

Create a custom typeface and scaler to render simple paths the
same on all platforms.

GM tests are modified to explicitly select the custom typeface.

R=reed@google.com, mtklein@google.com, bungeman@google.com
TBR=reed

Author: caryclark@google.com

Review URL: https://codereview.chromium.org/348323003
diff --git a/gm/blurs.cpp b/gm/blurs.cpp
index 8a8949a..ad363e4 100644
--- a/gm/blurs.cpp
+++ b/gm/blurs.cpp
@@ -45,6 +45,7 @@
 
         SkPaint paint;
         paint.setAntiAlias(true);
+        sk_tool_utils::set_portable_typeface(&paint);
         paint.setTextSize(SkIntToScalar(25));
         canvas->translate(SkIntToScalar(-40), SkIntToScalar(0));