Add Per-Monitor DPI Switches for Windows 10

chrome/app/chrome_exe_main_win.cc

 // Copyright (c) 2011 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 <windows.h>
 #include <malloc.h>
 #include <shellscalingapi.h>
 #include <stddef.h>
 #include <tchar.h>
 
@@ skipping 109 matching lines @@
   typedef BOOL(WINAPI *SetProcessDPIAwarePtr)(VOID);
   SetProcessDPIAwarePtr set_process_dpi_aware_func =
       reinterpret_cast<SetProcessDPIAwarePtr>(
       GetProcAddress(GetModuleHandleA("user32.dll"),
                       "SetProcessDPIAware"));
   return set_process_dpi_aware_func &&
     set_process_dpi_aware_func();
 }
 
 void EnableHighDPISupport() {
-  if (!SetProcessDpiAwarenessWrapper(PROCESS_SYSTEM_DPI_AWARE)) {
+  // Enable per-monitor DPI for Win10 or above instead of Win8.1 since Win8.1
+  // does not have EnableChildWindowDpiMessage, necessary for correct non-client
+  // area scaling across monitors.
+  bool allowed_platform = base::win::GetVersion() >= base::win::VERSION_WIN10;
+  const base::CommandLine* command_line =
+      base::CommandLine::ForCurrentProcess();
+  bool per_monitor_dpi_switch =
+      command_line->HasSwitch(switches::kEnablePerMonitorDpi) &&
+      !command_line->HasSwitch(switches::kDisablePerMonitorDpi);
+  PROCESS_DPI_AWARENESS process_dpi_awareness =
+      allowed_platform && per_monitor_dpi_switch
+          ? PROCESS_PER_MONITOR_DPI_AWARE
+          : PROCESS_SYSTEM_DPI_AWARE;
+  if (!SetProcessDpiAwarenessWrapper(process_dpi_awareness)) {
     SetProcessDPIAwareWrapper();
   }
 }
 
 // Returns true if |command_line| contains a /prefetch:# argument where # is in
 // [1, 8].
 bool HasValidWindowsPrefetchArgument(const base::CommandLine& command_line) {
   const base::char16 kPrefetchArgumentPrefix[] = L"/prefetch:";
 
   for (const auto& arg : command_line.argv()) {
@@ skipping 116 matching lines @@
   RemoveAppCompatFlagsEntry();
 
   // Load and launch the chrome dll. *Everything* happens inside.
   VLOG(1) << "About to load main DLL.";
   MainDllLoader* loader = MakeMainDllLoader();
   int rc = loader->Launch(instance);
   loader->RelaunchChromeBrowserWithNewCommandLineIfNeeded();
   delete loader;
   return rc;
 }