Add viz-host HitTestQuery.

components/viz/hit_test/query/hit_test_query.h

+// Copyright 2017 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.
+
+#ifndef COMPONENTS_VIZ_HIT_TEST_QUERY_HIT_TEST_QUERY_H_
+#define COMPONENTS_VIZ_HIT_TEST_QUERY_HIT_TEST_QUERY_H_
+
+#include <vector>
+
+#include "base/macros.h"
+#include "components/viz/hit_test/common/display_hit_test_data.h"
+#include "components/viz/hit_test/hit_test_export.h"
+#include "ui/gfx/geometry/point.h"
+
+namespace viz {
+namespace hit_test {
+
+struct Target {
+  cc::FrameSinkId id;
+  gfx::Point location_in_target;
+  // TODO(riajiang): use HitTestRegionFlags instead of int after
+  // https://codereview.chromium.org/2908783002/
+  int flags;
+};
+
+// Finds the target for a given location based on DisplayHitTestData aggreated
+// by HitTestComponent.
+class HIT_TEST_EXPORT HitTestQuery {

[rjkroege, 2017/06/12 17:17:24]

this needs eventually to dangle off of GpuHost. And you will multiple of them.
One per display. And they can come and go as displays are added and removed.

[riajiang, 2017/06/13 18:42:29]

Should GpuHost be the one that creates both the shmem and HitTestQuery?

+ public:
+  HitTestQuery();
+  ~HitTestQuery();
+
+  // TODO(riajiang): Read from shmem directly once it's set up. For now, use
+  // fake data.
+  void set_display_hit_test_data_list(

[rjkroege, 2017/06/12 17:17:24]

this is fakery that will go away?

[riajiang, 2017/06/13 18:42:29]

Yes. Once shmem is set up, we'll just read from there.

+      std::vector<DisplayHitTestData> display_hit_test_data_list) {
+    display_hit_test_data_list_ = display_hit_test_data_list;
+  }
+
+  // Find Target for |location_in_root|, including the FrameSinkId of the
+  // target, updated location in the coordinate system of the target and
+  // hit-test flags for the target.
+  Target FindTargetForLocation(const gfx::Point& location_in_root);

[rjkroege, 2017/06/12 17:17:24]

I may quibble at you about passing Target instances by value. Do they need to
mutable? One might return a const& if only one thread is accessing this class at
a time.

[riajiang, 2017/06/13 18:42:30]

True! They are not going to be mutable, changing to return a const&.

+
+ private:
+  std::vector<DisplayHitTestData> display_hit_test_data_list_;
+
+  DISALLOW_COPY_AND_ASSIGN(HitTestQuery);
+};
+
+}  // namespace hit_test
+}  // namespace viz
+
+#endif  // COMPONENTS_VIZ_HIT_TEST_QUERY_HIT_TEST_QUERY_H_