Individually enable and disable SkCodecs

public.bzl

Index: public.bzl
diff --git a/public.bzl b/public.bzl
index 32cb2de7864dfa04ba30db38dff496976b794648..bebadc66f508446acd93c19702feb7e8b01eae77 100644
--- a/public.bzl
+++ b/public.bzl
@@ -479,14 +479,22 @@ DEFINES_UNIX = [
     "SK_BUILD_FOR_UNIX",
     "SK_SAMPLES_FOR_X",
     "SK_SFNTLY_SUBSETTER",
+    "SK_CODEC_DECODES_GIF",
+    "SK_CODEC_DECODES_ICO",
+    "SK_CODEC_DECODES_JPEG",
+    "SK_CODEC_DECODES_PNG",
     "SK_CODEC_DECODES_RAW",
+    "SK_CODEC_DECODES_WEBP",
 ]
 
 DEFINES_ANDROID = [
     "SK_BUILD_FOR_ANDROID",
-    # TODO(benjaminwagner): Try to get png library updated?
-    "SK_PNG_NO_INDEX_SUPPORTED",
+    "SK_CODEC_DECODES_GIF",
+    "SK_CODEC_DECODES_ICO",
+    "SK_CODEC_DECODES_JPEG",
+    "SK_CODEC_DECODES_PNG",
     "SK_CODEC_DECODES_RAW",
+    "SK_CODEC_DECODES_WEBP",
 ]
 
 DEFINES_IOS = [
@@ -501,6 +509,10 @@ DEFINES_ALL = [
     "SK_USE_FREETYPE_EMBOLDEN",
     # Turn on a few Google3-specific build fixes.
     "GOOGLE3",
+    # There image codecs can be enabled on all platforms since
+    # they don't have any dependencies.
+    "SK_CODEC_DECODES_BMP",
+    "SK_CODEC_DECODES_WBMP",
 ]
 
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