Add viz-host HitTestQuery.

components/viz/hit_test/query/hit_test_query.cc

+// 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.
+
+#include "components/viz/hit_test/query/hit_test_query.h"
+
+namespace viz {
+namespace hit_test {
+
+HitTestQuery::HitTestQuery() {}
+
+HitTestQuery::~HitTestQuery() {}
+
+Target HitTestQuery::FindTargetForLocation(const gfx::Point& location_in_root) {
+  DCHECK(!display_hit_test_data_list_.empty());
+  Target confirmed_target_so_far;
+  Target tentative_target_so_far;
+  tentative_target_so_far.location_in_target = location_in_root;
+  for (uint32_t i = 0; i < display_hit_test_data_list_.size(); ++i) {

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

there's a way to make a vector using a pre-defined buffer. might be worth doing.

+    DisplayHitTestData data = display_hit_test_data_list_[i];
+    if (data.bounds.Contains(tentative_target_so_far.location_in_target)) {
+      if (!data.transform.IsIdentity()) {
+        DCHECK(data.transform.TransformPointReverse(

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

the statement inside the DCHECK is going to not execute in release. Please
define and document your expectations about the matrices. Also, where is the
code that multiplies the matrices together?

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

Ah I see! I'll move the transform out of DCHECK and just DCHECK the result.

The point would be transformed to the correct coordinate system after every
walk? So we don't really need to keep a stack of all the matrices? Or do you
mean we need the matrices for something else?

+            &tentative_target_so_far.location_in_target));
+      }
+      tentative_target_so_far.id = data.id;
+      tentative_target_so_far.flags = data.flags;
+      // TODO(riajiang): Check properly once HitTestRegionFlags is well defined
+      // after https://codereview.chromium.org/2908783002/.
+      // HIT_TEST_MINE is set to be true, which means it can receive events.
+      if (data.flags)
+        confirmed_target_so_far = tentative_target_so_far;
+      if (!data.child_count)
+        break;
+    } else {
+      i += data.child_count;
+    }
+  }
+  return confirmed_target_so_far;
+}
+
+}  // namespace hit_test
+}  // namespace viz