Simulate generic down/up key events to make AllowSetForegroundWindow …

…call succeed

Despite the fact that the Windows notification center grants the helper
permission to set the foreground window, the helper fails to pass the baton
to Chrome at an alarming rate; see https://crbug.com/837796.

Sending generic down/up key events seems to fix it.

Bug: 837796, 734095
Change-Id: I9b590d5149df35cfcb8219b0a386c5a9cfdb8eb0
Reviewed-on: https://chromium-review.googlesource.com/1192416
Commit-Queue: Xi Cheng <chengx@chromium.org>
Reviewed-by: Greg Thompson <grt@chromium.org>
Cr-Commit-Position: refs/heads/master@{#586968}

chrome/notification_helper/notification_activator.cc

@@ -4,6 +4,8 @@
 
 #include "chrome/notification_helper/notification_activator.h"
 
+#include <windows.h>
+
 #include <shellapi.h>
 
 #include "base/command_line.h"
@@ -143,6 +145,21 @@ HRESULT NotificationActivator::Activate(
   if (info.hProcess != nullptr) {
     base::Process process(info.hProcess);
     DWORD pid = ::GetProcessId(process.Handle());
+
+    // Despite the fact that the Windows notification center grants the helper
+    // permission to set the foreground window, the helper fails to pass the
+    // baton to Chrome at an alarming rate; see https://crbug.com/837796.
+    // Sending generic down/up key events seems to fix it.
+    INPUT keyboard_inputs[2] = {};
+
+    keyboard_inputs[0].type = INPUT_KEYBOARD;
+    keyboard_inputs[0].ki.dwFlags = 0;  // Key press.
+
+    keyboard_inputs[1] = keyboard_inputs[0];
+    keyboard_inputs[1].ki.dwFlags |= KEYEVENTF_KEYUP;  // key release.
+
+    ::SendInput(2, keyboard_inputs, sizeof(keyboard_inputs[0]));
+
     if (!::AllowSetForegroundWindow(pid)) {
 #if !defined(NDEBUG)
       DWORD error_code = ::GetLastError();