Fix bug that touch-dragging window to the display edge causes system crash

In current code, we have no constraints on gesture event's location.
As result, when window is dragged by touch-gestures to the edge of display,
gesture's location may be in a wrong display. It will lead to system crash.
In this CL, constraint on gesture event's location is added

Change-Id: I2c03d369df0b7bed143edb3f04a9c7aad5968d4a
Test: ash_unittests
Bug: 917060
Reviewed-on: https://chromium-review.googlesource.com/c/1413416
Commit-Queue: Andrew Xu <andrewxu@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#625716}

ash/wm/toplevel_window_event_handler_unittest.cc

@@ -524,6 +524,33 @@ TEST_F(ToplevelWindowEventHandlerTest, GestureDrag) {
             window_state->GetRestoreBoundsInScreen().ToString());
 }
 
+// Verifies that window dragged by touch-gestures to the edge of display
+// will not lead to system crash (see https://crbug.com/917060).
+TEST_F(ToplevelWindowEventHandlerTest, GestureDragMultiDisplays) {
+  UpdateDisplay("800x600, 800x600");
+  std::unique_ptr<aura::Window> target(CreateTestWindowInShellWithDelegate(
+      new TestWindowDelegate(HTCAPTION), 0, gfx::Rect(0, 0, 100, 100)));
+  wm::WindowState* window_state = wm::GetWindowState(target.get());
+  ui::test::EventGenerator generator(Shell::GetPrimaryRootWindow(),
+                                     target.get());
+  gfx::Rect old_bounds = target->bounds();
+  gfx::Point location(5, 5);
+  gfx::Point end = location;
+
+  // On real device, gesture event's location may not be accurate. For example,
+  // when window is dragged by touch-gestures to the edge of display, it may
+  // create gesture events with location out of the display bounds. Let |end| be
+  // out of the primary display's bounds to emulate this situation.
+  end.Offset(800, 0);
+  generator.GestureScrollSequence(location, end,
+                                  base::TimeDelta::FromMilliseconds(5), 10);
+
+  // Verify that the window has moved after the gesture.
+  EXPECT_NE(old_bounds.ToString(), target->bounds().ToString());
+  EXPECT_EQ(mojom::WindowStateType::RIGHT_SNAPPED,
+            window_state->GetStateType());
+}
+
 // Tests that a gesture cannot minimize an unminimizeable window.
 TEST_F(ToplevelWindowEventHandlerTest,
        GestureAttemptMinimizeUnminimizeableWindow) {

ash/wm/wm_toplevel_window_event_handler.cc

@@ -18,6 +18,7 @@
 #include "ui/aura/window_observer.h"
 #include "ui/base/hit_test.h"
 #include "ui/events/event.h"
+#include "ui/wm/core/coordinate_conversion.h"
 
 namespace ash {
 namespace wm {
@@ -312,10 +313,33 @@ void WmToplevelWindowEventHandler::OnGestureEvent(ui::GestureEvent* event,
     return;
 
   switch (event->type()) {
-    case ui::ET_GESTURE_SCROLL_UPDATE:
+    case ui::ET_GESTURE_SCROLL_UPDATE: {
+      gfx::Rect bounds_in_screen = target->GetRootWindow()->GetBoundsInScreen();
+      gfx::Point screen_location = event->location();
+      ::wm::ConvertPointToScreen(target, &screen_location);
+
+      // It is physically not possible to move a touch pointer from one display
+      // to another, so constrain the bounds to the display. This is important,
+      // as it is possible for touch points to extend outside the bounds of the
+      // display (as happens with gestures on the bezel), and dragging via touch
+      // should not trigger moving to a new display.(see
+      // https://crbug.com/917060)
+      if (!bounds_in_screen.Contains(screen_location)) {
+        int x = std::max(
+            std::min(screen_location.x(), bounds_in_screen.right() - 1),
+            bounds_in_screen.x());
+        int y = std::max(
+            std::min(screen_location.y(), bounds_in_screen.bottom() - 1),
+            bounds_in_screen.y());
+        gfx::Point updated_location(x, y);
+        ::wm::ConvertPointFromScreen(target, &updated_location);
+        event->set_location(updated_location);
+      }
+
       HandleDrag(target, event);
       event->StopPropagation();
       return;
+    }
     case ui::ET_GESTURE_SCROLL_END:
       // We must complete the drag here instead of as a result of ET_GESTURE_END
       // because otherwise the drag will be reverted when EndMoveLoop() is