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/bitmapscroll.cpp b/gm/bitmapscroll.cpp
index 7e23d8b..0015cd8 100644
--- a/gm/bitmapscroll.cpp
+++ b/gm/bitmapscroll.cpp
@@ -109,6 +109,7 @@
     void drawLabel(SkCanvas* canvas, const char *text, int startX, int startY,
                  int endX, int endY) {
         SkPaint paint;
+        sk_tool_utils::set_portable_typeface(&paint);
         paint.setColor(0xFF000000);
         SkPath path;
         path.moveTo(SkIntToScalar(startX), SkIntToScalar(startY));