Fix missing headers in WebKit/public:mojo_bindings

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 4a244fb5b11de7f387a8b454e9c5bedd861410f5..0c42bdd8e9f07df8d2353922a500749a2df4fc22 100644
--- a/mojo/public/tools/bindings/mojom.gni
+++ b/mojo/public/tools/bindings/mojom.gni
@@ -602,6 +602,9 @@ template("mojom") {
           deps += _typemap_config.deps
         }
       }
+      if (defined(invoker.export_header)) {
+        sources += [ "//" + invoker.export_header ]
+      }
       if (defined(bindings_configuration.for_blink) &&
           bindings_configuration.for_blink) {
         public_deps += [ "//mojo/public/cpp/bindings:wtf_support" ]