Clean up FreeType code for 2.3.8.

We already require FreeType 2.3.8 in order to compile and run.
Make this requirement explicit and take advantage of it.

Review URL: https://codereview.chromium.org/748063003
diff --git a/gyp/freetype.gyp b/gyp/freetype.gyp
index cd71e78..fc528d4 100644
--- a/gyp/freetype.gyp
+++ b/gyp/freetype.gyp
@@ -41,9 +41,9 @@
                       ],
                     },
                     'defines': [
-                      # The font host requires at least FreeType 2.3.0
-                      # at runtime.
-                      'SK_FONTHOST_FREETYPE_RUNTIME_VERSION=0x020300',
+                      # Skia's FreeType port requires at least FreeType 2.3.8
+                      # for building and at runtime.
+                      'SK_FONTHOST_FREETYPE_RUNTIME_VERSION=0x020308',
                       'SK_CAN_USE_DLOPEN=1',
                     ],
                   }