unbundle: add GN files for flac, harfbuzz-ng, and libwebp

build/linux/unbundle/libwebp.gn

Index: build/linux/unbundle/libwebp.gn
diff --git a/third_party/leakcanary/config.gni b/build/linux/unbundle/libwebp.gn
similarity index 70%
copy from third_party/leakcanary/config.gni
copy to build/linux/unbundle/libwebp.gn
index f6adcddf3ecc4442c7793666dfeecaf1f108fea8..217911167b95466b4a64790f4cff7449da4a7253 100644
--- a/third_party/leakcanary/config.gni
+++ b/build/linux/unbundle/libwebp.gn
@@ -2,6 +2,9 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-declare_args() {
-  enable_leakcanary = false
+source_set("libwebp") {
+  libs = [
+    "webp",
+    "webpdemux",
+  ]
 }