Add a BUILD target and a script to build a public static library for ios/web_view.

ios/web_view/BUILD.gn

Index: ios/web_view/BUILD.gn
diff --git a/ios/web_view/BUILD.gn b/ios/web_view/BUILD.gn
index 1755748783f025fd9447a2945e68dbeaa39c27f5..e93b94e8a5c859dc3eaf145e7df071a9a90dcc1e 100644
--- a/ios/web_view/BUILD.gn
+++ b/ios/web_view/BUILD.gn
@@ -12,3 +12,18 @@ group("web_view") {
     "//ios/web_view/internal",
   ]
 }
+
+# Build and use this .a file to use this library in apps outside Chromium
+# code base. This is a complete static library (containing all dependencies),
+# and it doesn't expose internal symbols to reduce risk of symbol conflict.
+copy("lib_web_view") {
+  deps = [
+    "//ios/web_view/internal:lib_web_view",
+  ]
+  sources = [
+    "$target_out_dir/internal/libweb_view.a",
+  ]
+  outputs = [
+    "$target_out_dir/libweb_view.a",
+  ]
+}