[mojo] Add Mojo bindings support for IPC::ParamTraits

mojo/public/cpp/bindings/lib/pickle_buffer.h

Index: mojo/public/cpp/bindings/lib/pickle_buffer.h
diff --git a/mojo/public/cpp/bindings/lib/pickle_buffer.h b/mojo/public/cpp/bindings/lib/pickle_buffer.h
index 4b1486086283c01a67a4bc8413131796f1ae5c51..994738f2150a7667660cd0cdad4bbbd1b82ab58f 100644
--- a/mojo/public/cpp/bindings/lib/pickle_buffer.h
+++ b/mojo/public/cpp/bindings/lib/pickle_buffer.h
@@ -38,6 +38,9 @@ class PickleBuffer : public base::Pickle, public Buffer {
   // Resizes the underlying Pickle's capacity without zeroing.
   void AllocUninitializedData(uint32_t num_bytes);
 
+  // Buffer:
+  PickleBuffer* AsPickleBuffer() override;
+
  private:
   // Buffer implementation. Note that this may grow the Pickle's capacity if
   // necessary, but you can avoid this by calling AllocData to preallocate when