move imagefilters into separate dir and flag for build.gn

Requires https://chromium-review.googlesource.com/c/chromium/src/+/1105062

Bug: skia:
Change-Id: I948056234efa57c0f727a61d5fb3258034de5199
Reviewed-on: https://skia-review.googlesource.com/135566
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Reed <reed@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index 94ac8f5..3f58f44 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -34,6 +34,7 @@
   skia_android_serial = ""
   skia_enable_discrete_gpu = true
   skia_enable_effects = true
+  skia_enable_effects_imagefilters = true
   skia_enable_flutter_defines = false
   skia_enable_fontmgr_empty = false
   skia_enable_gpu = true
@@ -371,7 +372,15 @@
   ]
   sources =
       skia_effects_sources + [ "src/ports/SkGlobalInitialization_default.cpp" ]
-  sources_when_disabled = [ "src/ports/SkGlobalInitialization_none.cpp" ]
+  if (skia_enable_effects_imagefilters) {
+    sources += skia_effects_imagefilter_sources
+  } else {
+    sources += [ "src/ports/SkGlobalInitialization_none_imagefilters.cpp" ]
+  }
+  sources_when_disabled = [
+    "src/ports/SkGlobalInitialization_none.cpp",
+    "src/ports/SkGlobalInitialization_none_imagefilters.cpp",
+  ]
 }
 
 optional("fontmgr_android") {