[Switch Access] Use source_device_id to identify physical key events.

This addresses a bug in Switch Access (go/cros-switch) where users got
stuck in editable text fields. The root cause was that the physical key
events were perceived to be virtual key events by the Switch Access
event handler. The solution is to more precisely identify which key
events come from physical devices.

Bug: 996893
Change-Id: Id39130ce7edc7f933c1be43f434b5a08f909f19f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1804395
Commit-Queue: Anastasia Helfinstein <anastasi@google.com>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#699053}

ash/events/switch_access_event_handler.cc

@@ -8,6 +8,8 @@
 #include "ash/public/cpp/switch_access_event_handler_delegate.h"
 #include "ash/shell.h"
 #include "ui/events/event.h"
+#include "ui/events/event_constants.h"
+#include "ui/events/event_utils.h"
 
 namespace ash {
 
@@ -101,8 +103,17 @@ void SwitchAccessEventHandler::OnKeyEvent(ui::KeyEvent* event) {
 bool SwitchAccessEventHandler::ShouldCancelEvent(
     const ui::KeyEvent& event) const {
   // Ignore virtual key events so users can type with the onscreen keyboard.
-  if (ignore_virtual_key_events_ && !event.HasNativeEvent())
-    return false;
+  if (ignore_virtual_key_events_ &&
+      event.source_device_id() == ui::ED_UNKNOWN_DEVICE) {
+    // When running Chrome OS on Linux, the source_device_id property is never
+    // populated.
+    auto* properties = event.properties();
+    bool is_linux_xevent =
+        properties &&
+        properties->find(ui::kPropertyKeyboardIBusFlag) != properties->end();
+    if (!is_linux_xevent)
+      return false;
+  }
 
   if (forward_key_events_)
     return true;