IPC::Message -> base::Pickle

This changes consumers of IPC::Message to generally refer
refer to base::Pickle instead when performing serialization
and deserialization operations. The few specific instances
where the IPC::Message interface (Read/WriteAttachent) is
needed can safely be static_cast'd, as IPC::Message is the
only public subclass of base::Pickle.

The purpose of this change is to facilitate the transition
to Mojo IPC, as we've trained the Mojo bindings layer to
use existing ParamTraits<T> parameterized over base::Pickle.

To support this base::Pickle has had some stub interfaces
added for WriteAttachment and ReadAttachment, along with a
Pickle::Attachment.

A follow-up patch will add sizing traits to the standard
IPC_STRUCT macros, enabling the majority of Chrome IPC
structs to be carried over Mojo message pipes as-is.

BUG=577685
R=jam@chromium.org

Review URL: https://codereview.chromium.org/1659003003

Cr-Commit-Position: refs/heads/master@{#373323}

1 files changed, 3 insertions, 2 deletions

diff --git a/printing/pdf_render_settings.h b/printing/pdf_render_settings.h
index a2e182e..5c5542a 100644
--- a/printing/pdf_render_settings.h
+++ b/printing/pdf_render_settings.h
@@ -36,13 +36,14 @@ namespace IPC {
 template <>
 struct ParamTraits<printing::PdfRenderSettings> {
   typedef printing::PdfRenderSettings param_type;
-  static void Write(Message* m, const param_type& p) {
+  static void Write(base::Pickle* m, const param_type& p) {
     WriteParam(m, p.area_);
     WriteParam(m, p.dpi_);
     WriteParam(m, p.autorotate_);
   }
 
-  static bool Read(const Message* m, base::PickleIterator* iter,
+  static bool Read(const base::Pickle* m,
+                   base::PickleIterator* iter,
                    param_type* r) {
     return ReadParam(m, iter, &r->area_) &&
         ReadParam(m, iter, &r->dpi_) &&