Make it possible to inherit from any constructable host object

Make it possible to inherit from any constructable host object

This CL makes it possible for authors to extend any host object (e.g., DOM
objects) and to use those objects in all the usual places they can be used in
the API.

R=esprehn@chromium.org

Committed: https://chromium.googlesource.com/external/mojo/+/cfb583a26e7415b26c28cab38dde1bd87d68c4cd

[esprehn, 2015-02-20 06:56:10]

lgtm, I'm not super familiar with the generator but it looks okay. What's the
one_based stuff about though?

https://codereview.chromium.org/936193005/diff/40001/sky/engine/tonic/dart_wr...
File sky/engine/tonic/dart_wrappable.cc (right):

https://codereview.chromium.org/936193005/diff/40001/sky/engine/tonic/dart_wr...
sky/engine/tonic/dart_wrappable.cc:52: args, 0, kNumberOfNativeFields,
native_fields)));
So all things have the same number of native fields?

[abarth-chromium, 2015-02-20 07:00:34]

> What's the one_based stuff about though?

For non-static functions, the 0th argument is the "receiver" (aka |this|).  For
static functions, there is no receiver, which means the 0th argument is the
first one the caller supplied.

Previously, we generated _constructor functions that were static because they
called into C++, which malloced the Dart object and returned it through the
"factory" constructor.  With this CL, we ditch factory constructors and have the
DartVM malloc up the Dart object.  We then add the backing C++ object when the
base class's constructor runs.

The net result of that approach is that the _constructor function is now a
member function instead of a static function.  That means we need to apply the
same argument number fixup that we use for normal methods because we're getting
the half-constructed |this| object as the 0th argument.

https://codereview.chromium.org/936193005/diff/40001/sky/engine/tonic/dart_wr...
File sky/engine/tonic/dart_wrappable.cc (right):

https://codereview.chromium.org/936193005/diff/40001/sky/engine/tonic/dart_wr...
sky/engine/tonic/dart_wrappable.cc:52: args, 0, kNumberOfNativeFields,
native_fields)));
On 2015/02/20 at 06:56:10, esprehn wrote:
> So all things have the same number of native fields?

Yes.  Always two there are.

[abarth-chromium, 2015-02-20 07:01:22]

On 2015/02/20 at 07:00:34, abarth wrote:
> Yes.  Always two there are.

One is the backing C++ object and the other is an RTTI-like object with metadata
about the runtime type of the object for the bindings to use.

[abarth-chromium, 2015-02-20 07:09:56]

Committed patchset #3 (id:40001) manually as
cfb583a26e7415b26c28cab38dde1bd87d68c4cd (presubmit successful).