Build custom empty SkFontMgr for Android Framework

Bug: b/118742766

The Android Framework does not need SkFontMgr_android*. Switch it to
using SkFontMgr_custom*. This will also be the SkFontMgr to use when
we're building Skia as a host-side library.

BUILD.gn:
- Rename fontmgr_fuchsia to fontmgr_custom_empty so it can be selected
  specifically by the Android Framework build. Default condition is
  unchanged, so fuchsia will still build it.
- Similarly, create a new argument for fontmgr_android and
  fontmgr_custom, so they can be omitted by the Android Framework build.
  Again, default condition is unchanged, so no other builds should be
  affected.

gn_to_bp.py:
- Set the new arguments to build the files we want.

Change-Id: Ic85db8acd64f625b00fe2c9bc451ae8814d97a59
Reviewed-on: https://skia-review.googlesource.com/c/170725
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Leon Scroggins <scroggo@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index a2052c8..02bb2e0 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -43,7 +43,6 @@
   skia_enable_ccpr = true
   skia_enable_nvpr = !skia_enable_flutter_defines
   skia_enable_discrete_gpu = true
-  skia_enable_fontmgr_empty = false
   skia_enable_gpu = true
   skia_enable_nima = false
   skia_enable_pdf = true
@@ -69,6 +68,11 @@
   skia_use_dng_sdk = !is_fuchsia && skia_use_libjpeg_turbo && skia_use_zlib
   skia_use_sfntly = skia_use_icu
   skia_enable_atlas_text = is_skia_dev_build && skia_enable_gpu
+  skia_enable_fontmgr_empty = false
+  skia_enable_fontmgr_custom = (is_linux || target_cpu == "wasm") &&
+                               skia_use_freetype && !skia_use_fontconfig
+  skia_enable_fontmgr_custom_empty = is_fuchsia && skia_use_freetype
+  skia_enable_fontmgr_android = skia_use_expat && skia_use_freetype
 
   if (is_android) {
     skia_use_vulkan = defined(ndk_api) && ndk_api >= 24
@@ -92,8 +96,6 @@
 # Our tools require static linking (they use non-exported symbols), and the GPU backend.
 skia_enable_tools = skia_enable_tools && !is_component_build && skia_enable_gpu
 
-fontmgr_android_enabled = skia_use_expat && skia_use_freetype
-
 skia_public_includes = [
   "include/android",
   "include/c",
@@ -379,7 +381,7 @@
 }
 
 optional("fontmgr_android") {
-  enabled = fontmgr_android_enabled
+  enabled = skia_enable_fontmgr_android
 
   deps = [
     ":typeface_freetype",
@@ -393,8 +395,7 @@
 }
 
 optional("fontmgr_custom") {
-  enabled = (is_linux || target_cpu == "wasm") && skia_use_freetype &&
-            !skia_use_fontconfig
+  enabled = skia_enable_fontmgr_custom
 
   deps = [
     ":typeface_freetype",
@@ -433,8 +434,8 @@
   ]
 }
 
-optional("fontmgr_fuchsia") {
-  enabled = is_fuchsia && skia_use_freetype
+optional("fontmgr_custom_empty") {
+  enabled = skia_enable_fontmgr_custom_empty
 
   deps = [
     ":typeface_freetype",
@@ -849,9 +850,9 @@
     ":crc32",
     ":fontmgr_android",
     ":fontmgr_custom",
+    ":fontmgr_custom_empty",
     ":fontmgr_empty",
     ":fontmgr_fontconfig",
-    ":fontmgr_fuchsia",
     ":heif",
     ":hsw",
     ":jpeg",
@@ -1519,7 +1520,7 @@
   test_lib("tests") {
     public_include_dirs = [ "tests" ]
     sources = tests_sources + pathops_tests_sources
-    if (!fontmgr_android_enabled) {
+    if (!skia_enable_fontmgr_android) {
       sources -= [ "//tests/FontMgrAndroidParserTest.cpp" ]
     }
     if (!(skia_use_freetype && skia_use_fontconfig)) {