Mojo message validation tests: add integration tests and move existing conformance tests.

mojo/mojo_public.gypi

 {
   'targets': [
     {
       'target_name': 'mojo_system',
       'type': 'static_library',
       'defines': [
         'MOJO_SYSTEM_IMPLEMENTATION',
       ],
       'include_dirs': [
         '..',
@@ skipping 285 matching lines @@
       'target_name': 'mojo_public_test_interfaces',
       'type': 'static_library',
       'sources': [
         'public/interfaces/bindings/tests/math_calculator.mojom',
         'public/interfaces/bindings/tests/sample_factory.mojom',
         'public/interfaces/bindings/tests/sample_import.mojom',
         'public/interfaces/bindings/tests/sample_import2.mojom',
         'public/interfaces/bindings/tests/sample_interfaces.mojom',
         'public/interfaces/bindings/tests/sample_service.mojom',
         'public/interfaces/bindings/tests/test_structs.mojom',
+        'public/interfaces/bindings/tests/validation_test_interfaces.mojom',
       ],
       'includes': [ 'public/tools/bindings/mojom_bindings_generator.gypi' ],
       'export_dependent_settings': [
         'mojo_cpp_bindings',
       ],
       'dependencies': [
         'mojo_cpp_bindings',
       ],
     },
     {
@@ skipping 108 matching lines @@
           },
           'dependencies': [
             'mojo_public_java',
           ],
           'includes': [ '../build/java.gypi' ],
         },
       ],
     }],
   ],
 }