add platform_font_manager()

This string replaces {major_}platform_os_name() and
platform_extra_config() for the font-focused GMs using them.

The GDI bots will report "GDI", the NativeFont bots their OS,
and other bots "".

Change-Id: I8f7bb1ffea3cc91601c98b4ccff7a3a234ac77d3
Reviewed-on: https://skia-review.googlesource.com/70500
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
diff --git a/gm/fontmgr.cpp b/gm/fontmgr.cpp
index 9708d19..b604175 100644
--- a/gm/fontmgr.cpp
+++ b/gm/fontmgr.cpp
@@ -65,8 +65,7 @@
         } else {
             fFM = SkFontMgr::RefDefault();
         }
-        fName.append(sk_tool_utils::platform_os_name());
-        fName.append(sk_tool_utils::platform_extra_config("GDI"));
+        fName.append(sk_tool_utils::platform_font_manager());
     }
 
 protected:
@@ -134,8 +133,7 @@
 protected:
     SkString onShortName() override {
         SkString name("fontmgr_match");
-        name.append(sk_tool_utils::platform_os_name());
-        name.append(sk_tool_utils::platform_extra_config("GDI"));
+        name.append(sk_tool_utils::platform_font_manager());
         return name;
     }
 
@@ -223,8 +221,7 @@
         if (scale != 1 || skew != 0) {
             fName.appendf("_%g_%g", scale, skew);
         }
-        fName.append(sk_tool_utils::platform_os_name());
-        fName.append(sk_tool_utils::platform_extra_config("GDI"));
+        fName.append(sk_tool_utils::platform_font_manager());
         fFM = SkFontMgr::RefDefault();
     }