Implement cc::FilterOperation StructTraits

cc/ipc/filter_operation.mojom

Index: cc/ipc/filter_operation.mojom
diff --git a/cc/ipc/filter_operation.mojom b/cc/ipc/filter_operation.mojom
new file mode 100644
index 0000000000000000000000000000000000000000..6bcb0733cc1b7887241537b1edfd88dc97d526d3
--- /dev/null
+++ b/cc/ipc/filter_operation.mojom
@@ -0,0 +1,40 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+module cc.mojom;
+
+import "skia/public/interfaces/image_filter.mojom";
+import "ui/gfx/geometry/mojo/geometry.mojom";
+
+enum FilterType {
+  GRAYSCALE,
+  SEPIA,
+  SATURATE,
+  HUE_ROTATE,
+  INVERT,
+  BRIGHTNESS,
+  CONTRAST,
+  OPACITY,
+  BLUR,
+  DROP_SHADOW,
+  COLOR_MATRIX,
+  ZOOM,
+  REFERENCE,
+  SATURATING_BRIGHTNESS,  // Not used in CSS/SVG.
+  ALPHA_THRESHOLD,  // Not used in CSS/SVG.
+  FILTER_TYPE_LAST = ALPHA_THRESHOLD
+};
+
+// See cc/output/filter_operation.h.
+struct FilterOperation {
+  FilterType type;
+  float amount;
+  gfx.mojom.Point? drop_shadow_offset;

[yzshen1, 2016/06/08 16:25:16]

the custom type gfx::Point doesn't support null state (i.e., the StructTraits
doesn't have IsNull/SetToNull), therefore, you need to use non-nullable type
(without the question mark) here. Otherwise, when bindings of a different
language sends us a null |drop_shadow_offset|, the deserialization will fail.

[Fady Samuel, 2016/06/08 17:04:19]

I've made it non-optional for now, but really it should be optional I think
because we don't always need to send it. I can investigate this optimization
separately.

[yzshen1, 2016/06/08 17:09:51]

One way is to make the custom type support null state.

Another possible solution is to map nullable and non-nullable types differently:
mojom.Point -> gfx::Piont mojom.Point? -> base::Optional<gfx::Point>. But that
is just an idea that we haven't determined to add support for.

+  uint32 drop_shadow_color;
+  skia.mojom.ImageFilter? image_filter;

[yzshen1, 2016/06/08 16:25:16]

Ditto.

[Fady Samuel, 2016/06/08 17:04:19]

Done.

+  array<float, 20>? matrix;
+  int32 zoom_inset;
+  // Note: SkRegion is currently not needed for serialization.
+};
+