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

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

This adds the ability to map mojom struct declarations
to native types (with either chromium or blink variants),
using IPC::ParamTraits definitions to prescribe
serialization behavior.

Existing ParamTraits declarations still must be modified
to use a base::Pickle instead of IPC::Message for Write,
but this can be done on a case-by-case basis as needed
and does not need to be applied universally across the
codebase.

Part of a series of changes to reuse existing serialization
traits with new Mojo bindings:

  1. https://codereview.chromium.org/1524613002
  2. https://codereview.chromium.org/1515423002
  3. https://codereview.chromium.org/1517043004
  4. This CL

BUG=

[Ken Rockot(use gerrit already), 2015-12-12 04:50:50]

Description was changed from

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

This adds the ability to map mojom struct declarations
to native types (with either chromium or blink variants),
using IPC::ParamTraits definitions to prescribe
serialization behavior.

Existing ParamTraits declarations still must be modified
to use a base::Pickle instead of IPC::Message for Write,
but this can be done on a case-by-case basis as needed
and does not need to be applied universally across the
codebase.

BUG=
==========

to

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

This adds the ability to map mojom struct declarations
to native types (with either chromium or blink variants),
using IPC::ParamTraits definitions to prescribe
serialization behavior.

Existing ParamTraits declarations still must be modified
to use a base::Pickle instead of IPC::Message for Write,
but this can be done on a case-by-case basis as needed
and does not need to be applied universally across the
codebase.

Part of a series of changes to reuse existing serialization
traits with new Mojo bindings:

  1. https://codereview.chromium.org/1524613002
  2. https://codereview.chromium.org/1515423002
  3. https://codereview.chromium.org/1517043004
  4. This CL

BUG=
==========