Reduce boilerplate when creating simple mojom::URLLoaders.

mojo/public/cpp/system/data_pipe.h

Index: mojo/public/cpp/system/data_pipe.h
diff --git a/mojo/public/cpp/system/data_pipe.h b/mojo/public/cpp/system/data_pipe.h
index 0dbc3c74e5e62c1d01f48ba68947726d66e899f9..9f58c27c3300a3b28098b876123ed3b33c576ad2 100644
--- a/mojo/public/cpp/system/data_pipe.h
+++ b/mojo/public/cpp/system/data_pipe.h
@@ -134,6 +134,7 @@ inline MojoResult EndReadDataRaw(DataPipeConsumerHandle data_pipe_consumer,
 class DataPipe {
  public:
   DataPipe();
+  explicit DataPipe(uint32_t capacity_num_bytes);
   explicit DataPipe(const MojoCreateDataPipeOptions& options);
   ~DataPipe();
 
@@ -148,6 +149,19 @@ inline DataPipe::DataPipe() {
   DCHECK_EQ(MOJO_RESULT_OK, result);
 }
 
+inline DataPipe::DataPipe(uint32_t capacity_num_bytes) {
+  MojoCreateDataPipeOptions options;
+  options.struct_size = sizeof(MojoCreateDataPipeOptions);
+  options.flags = MOJO_CREATE_DATA_PIPE_OPTIONS_FLAG_NONE;
+  options.element_num_bytes = 1;
+  options.capacity_num_bytes = capacity_num_bytes;
+  mojo::DataPipe data_pipe(options);
+  MojoResult result =
+      CreateDataPipe(&options, &producer_handle, &consumer_handle);
+  ALLOW_UNUSED_LOCAL(result);
+  DCHECK_EQ(MOJO_RESULT_OK, result);
+}
+
 inline DataPipe::DataPipe(const MojoCreateDataPipeOptions& options) {
   MojoResult result =
       CreateDataPipe(&options, &producer_handle, &consumer_handle);