C++ bindings: separate out serialization source set, have "mojom" targets optionally use serializat…

mojo/public/tools/bindings/mojom.gni

Index: mojo/public/tools/bindings/mojom.gni
diff --git a/mojo/public/tools/bindings/mojom.gni b/mojo/public/tools/bindings/mojom.gni
index 0c0f294c5c5d5ad5ca8a7b08e48a52dae8f155a2..6b0ad4ae5fd09b02975f9dc75a7c57deac3f644e 100644
--- a/mojo/public/tools/bindings/mojom.gni
+++ b/mojo/public/tools/bindings/mojom.gni
@@ -191,6 +191,10 @@ template("mojom") {
         rebase_path(root_gen_dir),
       ]
 
+      if (defined(invoker.dataonly) && invoker.dataonly) {
+        args += [ "--cpp_dataonly" ]
+      }
+
       if (defined(invoker.import_dirs)) {
         foreach(import_dir, invoker.import_dirs) {
           args += [
@@ -216,7 +220,14 @@ template("mojom") {
     public_configs =
         rebase_path([ "mojo/public/build/config:mojo_sdk" ], ".", mojo_root)
 
-    public_deps = rebase_path([ "mojo/public/cpp/bindings" ], ".", mojo_root)
+    if (defined(invoker.dataonly) && invoker.dataonly) {
+      public_deps = rebase_path([ "mojo/public/cpp/bindings:serialization" ],
+                                ".",
+                                mojo_root)
+    } else {
+      public_deps = rebase_path([ "mojo/public/cpp/bindings" ], ".", mojo_root)
+    }
+
     if (defined(invoker.sources)) {
       public_deps += [ ":${cpp_sources_target_name}" ]
     }