First pass on blink compiling for GN build

Source/BUILD.gn

Index: Source/BUILD.gn
diff --git a/Source/BUILD.gn b/Source/BUILD.gn
index 309b316f77e24ec1982f42f527d54a79db1fece6..4644b8fa0e1c6544a1ab5c75e16e736ef4a4f96c 100644
--- a/Source/BUILD.gn
+++ b/Source/BUILD.gn
@@ -10,58 +10,7 @@ if (is_clang) {
 # features ---------------------------------------------------------------------
 
 config("features") {
-  defines = [
-    "ENABLE_CUSTOM_SCHEME_HANDLER=0",
-    "ENABLE_SVG_FONTS=1",
-  ]
-
-  if (is_debug) {
-    # TODO(GYP) this should also be set when release_valgrind_build is set,
-    # but we don't have that flag in the GN build yet.
-    defines += [ "WTF_USE_DYNAMIC_ANNOTATIONS=1" ]
-  }
-
-  if (use_concatenated_impulse_responses) {
-    defines += [ "WTF_USE_CONCATENATED_IMPULSE_RESPONSES=1" ]
-  }
-
-  if (is_android) {
-    defines += [
-      "ENABLE_FAST_MOBILE_SCROLLING=1",
-      "ENABLE_MEDIA_CAPTURE=1",
-    ]
-  } else {
-    defines += [
-      "ENABLE_INPUT_MULTIPLE_FIELDS_UI=1",
-      "ENABLE_MEDIA_CAPTURE=0",
-      "ENABLE_WEB_AUDIO=1",
-    ]
-  }
-
-  if (use_webaudio_ffmpeg) {
-    defines += [ "WTF_USE_WEBAUDIO_FFMPEG=1" ]
-  }
-
-  if (use_openmax_dl_fft) {
-    defines += [
-      "WTF_USE_WEBAUDIO_OPENMAX_DL_FFT=1",
-      # Enabling the FFT is enough to enable WebAudio support to
-      # allow most WebAudio features to work on Android.
-      "ENABLE_WEB_AUDIO=1",
-    ]
-  }
-
-  if (!is_mac) {
-    # Mac OS X has not implemented support for ENABLE(OPENTYPE_VERTICAL) yet.
-    defines += [ "ENABLE_OPENTYPE_VERTICAL=1" ]
-  }
-
-  if (use_default_render_theme) {
-    defines += [ "WTF_USE_DEFAULT_RENDER_THEME=1" ]
-  }
-  if (enable_oilpan) {
-    defines += [ "ENABLE_OILPAN=1" ]
-  }
+  defines = feature_defines_list
 }
 
 # config -----------------------------------------------------------------------