Add ops warpper (open-mmlab#3457)

* Add ops warpper

* Reformat

* disable yapf

* Add comments

Author: ZwwWayne

.dev_scripts/linter.sh

@@ -1,3 +1,3 @@
-yapf -r -i --style mmdet/ configs/ tests/ tools/
+yapf -r -i mmdet/ configs/ tests/ tools/
 isort -rc mmdet/ configs/ tests/ tools/
 flake8 .

mmdet/ops/__init__.py

@@ -0,0 +1,32 @@
+# This file is added for back-compatibility. Thus, downstream codebase
+# could still use and import mmdet.ops.
+
+# yapf: disable
+from mmcv.ops import (ContextBlock, Conv2d, ConvTranspose2d, ConvWS2d,
+                      CornerPool, DeformConv, DeformConvPack, DeformRoIPooling,
+                      DeformRoIPoolingPack, GeneralizedAttention, Linear,
+                      MaskedConv2d, MaxPool2d, ModulatedDeformConv,
+                      ModulatedDeformConvPack, ModulatedDeformRoIPoolingPack,
+                      NonLocal2D, RoIAlign, RoIPool, SAConv2d,
+                      SigmoidFocalLoss, SimpleRoIAlign, batched_nms,
+                      build_plugin_layer, conv_ws_2d, deform_conv,
+                      deform_roi_pooling, get_compiler_version,
+                      get_compiling_cuda_version, modulated_deform_conv, nms,
+                      nms_match, point_sample, rel_roi_point_to_rel_img_point,
+                      roi_align, roi_pool, sigmoid_focal_loss, soft_nms)
+
+# yapf: enable
+
+__all__ = [
+    'nms', 'soft_nms', 'RoIAlign', 'roi_align', 'RoIPool', 'roi_pool',
+    'DeformConv', 'DeformConvPack', 'DeformRoIPooling', 'DeformRoIPoolingPack',
+    'ModulatedDeformRoIPoolingPack', 'ModulatedDeformConv',
+    'ModulatedDeformConvPack', 'deform_conv', 'modulated_deform_conv',
+    'deform_roi_pooling', 'SigmoidFocalLoss', 'sigmoid_focal_loss',
+    'MaskedConv2d', 'ContextBlock', 'GeneralizedAttention', 'NonLocal2D',
+    'get_compiler_version', 'get_compiling_cuda_version', 'ConvWS2d',
+    'conv_ws_2d', 'build_plugin_layer', 'batched_nms', 'Conv2d',
+    'ConvTranspose2d', 'MaxPool2d', 'Linear', 'nms_match', 'CornerPool',
+    'point_sample', 'rel_roi_point_to_rel_img_point', 'SimpleRoIAlign',
+    'SAConv2d'
+]