Improve compiler output for users who forget to include TypeConverter specializations.

Improve compiler output for users who forget to include TypeConverter specializations.

Currently when users forget to include their TypeConverter specializations, they get errors about various methods not defined in TypeConverter<x, y>. By removing the definition of the general template, users will get errors about incomplete type TypeConverter<x, y> used.

TEST=None
BUG=None

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=272054

[yzshen1, 2014-05-21 07:16:39]

Hi, Darin.

Would you please take a look? Thanks!

I decided to simply remove the definition of the general TypeConverter template.
If users forget to include their specializations, they will get:
=========================
...
error: incomplete type ‘mojo::TypeConverter<mojo::Rect, PP_Rect>’ used in nested
name specifier
...
=========================

I tried to generate more specific errors. The only way I came up was to use the
"Substitution failure is not an error" technique:
  static T ConvertFrom(const U& input, Buffer* buf) {
    return T::Did_you_forget_to_include_you_TypeConverter_specialization;
  }
which generated the following error:
=========================
...
error: ‘Did_you_forget_to_include_you_TypeConverter_specialization’ is not a
member of ‘mojo::Rect’
...
=========================
I feel that it is not necessarily easier to understand, and it bloats the
general template with hacks.

[darin (slow to review), 2014-05-21 07:25:19]

lgtm

[darin (slow to review), 2014-05-21 07:25:26]

The CQ bit was checked by darin@chromium.org

[commit-bot: I haz the power, 2014-05-21 07:28:03]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/yzshen@chromium.org/294473010/1

[commit-bot: I haz the power, 2014-05-22 03:00:33]

Change committed as 272054