GN: make libwebp an optional dependency

BUILD.gn

 # Copyright 2016 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 declare_args() {
+  skia_use_libwebp = !is_fuchsia
 }
 
 skia_public_includes = [
   "include/android",
   "include/c",
   "include/codec",
   "include/config",
   "include/core",
   "include/effects",
   "include/gpu",
@@ skipping 40 matching lines @@
     "third_party/etc1",
     "third_party/ktx",
   ]
 
   defines = [
     "SK_GAMMA_APPLY_TO_A8",
 
     "SK_HAS_GIF_LIBRARY",
     "SK_HAS_JPEG_LIBRARY",
     "SK_HAS_PNG_LIBRARY",
-    "SK_HAS_WEBP_LIBRARY",
 
     # TODO(halcanary): make this the default; this is the value Android uses.
     "SK_SFNTLY_SUBSETTER=\"sample/chromium/font_subsetter.h\"",
 
     "TURBO_HAS_565",
     "TURBO_HAS_CROP",
     "TURBO_HAS_SKIP",
   ]
   if (is_linux) {
     defines += [ "SK_SAMPLES_FOR_X" ]
@@ skipping 98 matching lines @@
     cflags = [ "-msse4.2" ]
   }
 
   source_set("opts_avx") {
     configs += skia_library_configs
     sources = opts_gypi.avx_sources
     cflags = [ "-mavx" ]
   }
 }
 
+if (skia_use_libwebp) {
+  config("webp_config") {
+    defines = [ "SK_HAS_WEBP_LIBRARY" ]
+  }
+  source_set("webp") {
+    configs += skia_library_configs
+    all_dependent_configs = [ ":webp_config" ]
+    deps = [
+      "//third_party/libwebp",
+    ]
+    sources = [
+      "src/codec/SkWebpAdapterCodec.cpp",
+      "src/codec/SkWebpCodec.cpp",
+      "src/images/SkWEBPImageEncoder.cpp",
+    ]
+  }
+} else {
+  source_set("webp") {
+  }
+}
+
 component("skia") {
   public_configs = [ ":skia_public" ]
   configs += skia_library_configs
 
   deps = [
+    ":webp",
     "//third_party/expat",
     "//third_party/giflib",
     "//third_party/libjpeg-turbo:libjpeg",
     "//third_party/libpng",
-    "//third_party/libwebp",
     "//third_party/sfntly",
     "//third_party/zlib",
   ]
   if (is_x86) {
     deps += [
       ":opts_avx",
       ":opts_sse2",
       ":opts_sse41",
       ":opts_sse42",
       ":opts_ssse3",
@@ skipping 27 matching lines @@
     "src/codec/SkJpegCodec.cpp",
     "src/codec/SkJpegDecoderMgr.cpp",
     "src/codec/SkJpegUtility.cpp",
     "src/codec/SkMaskSwizzler.cpp",
     "src/codec/SkMasks.cpp",
     "src/codec/SkPngCodec.cpp",
     "src/codec/SkSampledCodec.cpp",
     "src/codec/SkSampler.cpp",
     "src/codec/SkSwizzler.cpp",
     "src/codec/SkWbmpCodec.cpp",
-    "src/codec/SkWebpAdapterCodec.cpp",
-    "src/codec/SkWebpCodec.cpp",
     "src/images/SkImageEncoder.cpp",
     "src/images/SkImageEncoder_Factory.cpp",
     "src/images/SkJPEGImageEncoder.cpp",
     "src/images/SkJPEGWriteUtility.cpp",
     "src/images/SkKTXImageEncoder.cpp",
     "src/images/SkPNGImageEncoder.cpp",
-    "src/images/SkWEBPImageEncoder.cpp",
     "src/ports/SkDiscardableMemory_none.cpp",
     "src/ports/SkGlobalInitialization_default.cpp",
     "src/ports/SkImageGenerator_skia.cpp",
     "src/ports/SkMemory_malloc.cpp",
     "src/ports/SkOSFile_stdio.cpp",
     "src/sfnt/SkOTTable_name.cpp",
     "src/sfnt/SkOTUtils.cpp",
     "src/svg/SkSVGCanvas.cpp",
     "src/svg/SkSVGDevice.cpp",
     "src/utils/mac/SkStream_mac.cpp",
@@ skipping 349 matching lines @@
       "tools/SkShaper_harfbuzz.cpp",
       "tools/using_skia_and_harfbuzz.cpp",
     ]
     deps = [
       ":skia",
       "//third_party/harfbuzz",
     ]
     testonly = true
   }
 }