Add Linux implementation of the platform view example

[robert-ancell]

No description provided.

[flutter-dashboard]

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[robert-ancell]

[robert-ancell]

(The screenshot shows the wrong window title - fixed in the branch).

[Hixie]

@robert-ancell Is this still on your radar?

[robert-ancell]

Yes, @cbracken please review!

[cbracken]

lgtm!

[robert-ancell]

Build is failing due to:

/b/s/w/ir/cache/clang/bin/clang++ -g  CMakeFiles/platform_view.dir/main.cc.o CMakeFiles/platform_view.dir/my_application.cc.o CMakeFiles/platform_view.dir/flutter/generated_plugin_registrant.cc.o -o intermediates_do_not_run/platform_view -L/b/s/w/ir/x/w/flutter/examples/platform_view/linux/flutter/ephemeral -Wl,-rpath,/b/s/w/ir/x/w/flutter/examples/platform_view/linux/flutter/ephemeral:  -lflutter_linux_gtk  /usr/lib/x86_64-linux-gnu/libgtk-3.so  /usr/lib/x86_64-linux-gnu/libgdk-3.so  /usr/lib/x86_64-linux-gnu/libpangocairo-1.0.so  /usr/lib/x86_64-linux-gnu/libpango-1.0.so  /usr/lib/x86_64-linux-gnu/libharfbuzz.so  /usr/lib/x86_64-linux-gnu/libatk-1.0.so  /usr/lib/x86_64-linux-gnu/libcairo-gobject.so  /usr/lib/x86_64-linux-gnu/libcairo.so  /usr/lib/x86_64-linux-gnu/libgdk_pixbuf-2.0.so  /usr/lib/x86_64-linux-gnu/libgio-2.0.so  /usr/lib/x86_64-linux-gnu/libgobject-2.0.so  /usr/lib/x86_64-linux-gnu/libglib-2.0.so && :
ld.lld: error: undefined symbol: fl_method_call_get_type
>>> referenced by fl_method_call.h:19 (/b/s/w/ir/x/w/flutter/examples/platform_view/linux/flutter/ephemeral/flutter_linux/fl_method_call.h:19)
>>>               CMakeFiles/platform_view.dir/my_application.cc.o:(FL_METHOD_CALL(void*))
clang-15: error: linker command failed with exit code 1 (use -v to see invocation)

For some reason the compiler must be optimizing this away, so I've made flutter/engine#43394 to ensure this symbol is exported. Other get_type() functions already have this change.

[robert-ancell]

The build fix has landed in the engine, will rebuild this PR once that engine is being used by Flutter.

[robert-ancell]

@gspencergoog is the Google testing failure an issue?

[gspencergoog]

It is broken, but I think it's an error from a previous PR in the queue: it doesn't look related to this PR at all. I'd try rebasing to HEAD and see if you can move to a state that builds.

[I'm not sure why you're the one that has bad luck here: this doesn't happen that often, I promise!]