Use clampTo instead of static_cast<int> for layerX/Y

Because we use static_cast<int> to cast from double to int we expose
ourselves to float-cast-overflow.
We use clampTo to make sure the result is in int limits.

MouseEvent: :layerX, MouseEvent::layerY are returned as integers.
Bug: 1164520
Change-Id: I0881323f5508b3f4d3fb2f3f73d6b138aa4202c9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2622870Reviewed-by: Robert Flack <flackr@chromium.org>
Reviewed-by: Mustaq Ahmed <mustaq@chromium.org>
Commit-Queue: Liviu Tinta <liviutinta@chromium.org>
Cr-Commit-Position: refs/heads/master@{#844536}

third_party/blink/renderer/core/events/mouse_event.cc

@@ -42,6 +42,7 @@
 #include "third_party/blink/renderer/platform/bindings/dom_wrapper_world.h"
 #include "third_party/blink/renderer/platform/bindings/script_state.h"
 #include "third_party/blink/renderer/platform/instrumentation/use_counter.h"
+#include "third_party/blink/renderer/platform/wtf/math_extras.h"
 
 namespace blink {
 
@@ -493,22 +494,14 @@ int MouseEvent::layerX() {
   if (!has_cached_relative_position_)
     ComputeRelativePosition();
 
-  // TODO(mustaq): Remove the PointerEvent specific code when mouse has
-  // fractional coordinates. See crbug.com/655786.
-
-  return IsPointerEvent() ? layer_location_.X()
-                          : static_cast<int>(layer_location_.X());
+  return clampTo<int, double>(layer_location_.X());
 }
 
 int MouseEvent::layerY() {
   if (!has_cached_relative_position_)
     ComputeRelativePosition();
 
-  // TODO(mustaq): Remove the PointerEvent specific code when mouse has
-  // fractional coordinates. See crbug.com/655786.
-
-  return IsPointerEvent() ? layer_location_.Y()
-                          : static_cast<int>(layer_location_.Y());
+  return clampTo<int, double>(layer_location_.Y());
 }
 
 double MouseEvent::offsetX() const {

third_party/blink/renderer/core/events/mouse_event_test.cc

@@ -9,6 +9,7 @@
 
 #include "testing/gtest/include/gtest/gtest.h"
 
+#include "third_party/blink/renderer/core/events/mouse_event_init.h"
 #include "third_party/blink/renderer/platform/geometry/double_point.h"
 #include "third_party/blink/renderer/platform/geometry/int_point.h"
 
@@ -16,6 +17,8 @@ namespace blink {
 
 class MouseEventScreenClientPagePositionTest
     : public ::testing::TestWithParam<std::tuple<double, double>> {};
+class MouseEventLayerPositionTest
+    : public ::testing::TestWithParam<std::tuple<double, double>> {};
 
 TEST_P(MouseEventScreenClientPagePositionTest, PositionAsExpected) {
   MouseEvent& mouse_event = *MouseEvent::Create();
@@ -57,4 +60,40 @@ INSTANTIATE_TEST_SUITE_P(
         std::make_tuple(std::numeric_limits<double>::max() - 1.45,
                         std::floor(std::numeric_limits<double>::max() -
                                    1.45))));
+
+TEST_P(MouseEventLayerPositionTest, LayerPositionAsExpected) {
+  DoublePoint input_layer_location(std::get<0>(GetParam()),
+                                   std::get<0>(GetParam()));
+  IntPoint expected_layer_location(std::get<1>(GetParam()),
+                                   std::get<1>(GetParam()));
+
+  MouseEventInit& mouse_event_init = *MouseEventInit::Create();
+  mouse_event_init.setClientX(input_layer_location.X());
+  mouse_event_init.setClientY(input_layer_location.Y());
+  MouseEvent mouse_event("mousedown", &mouse_event_init);
+
+  ASSERT_EQ(mouse_event.layerX(), expected_layer_location.X());
+  ASSERT_EQ(mouse_event.layerY(), expected_layer_location.Y());
+}
+
+INSTANTIATE_TEST_SUITE_P(
+    MouseEventLayerPositionNoOverflow,
+    MouseEventLayerPositionTest,
+    ::testing::Values(
+        std::make_tuple(std::numeric_limits<int>::min() * 1.0,
+                        std::numeric_limits<int>::min()),
+        std::make_tuple(std::numeric_limits<int>::min() * 1.0 - 1.45,
+                        std::numeric_limits<int>::min()),
+        std::make_tuple(std::numeric_limits<int>::max() * 1.0,
+                        std::numeric_limits<int>::max()),
+        std::make_tuple(std::numeric_limits<int>::max() * 1.0 + 1.45,
+                        std::numeric_limits<int>::max()),
+        std::make_tuple(std::numeric_limits<double>::lowest(),
+                        std::numeric_limits<int>::min()),
+        std::make_tuple(std::numeric_limits<double>::lowest() + 1.45,
+                        std::numeric_limits<int>::min()),
+        std::make_tuple(std::numeric_limits<double>::max(),
+                        std::numeric_limits<int>::max()),
+        std::make_tuple(std::numeric_limits<double>::max() - 1.45,
+                        std::numeric_limits<int>::max())));
 }  // namespace blink