Enable Per-Monitor Support for Windows 10

This allows Chrome to render at the native resolution on each display on
Windows 10.

BUG=426656,624672

Review-Url: https://codereview.chromium.org/2114503002
Cr-Commit-Position: refs/heads/master@{#403329}

chrome/app/chrome_exe_main_win.cc

@@ -127,7 +127,14 @@ BOOL SetProcessDPIAwareWrapper() {
 }
 
 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.
+  PROCESS_DPI_AWARENESS process_dpi_awareness =
+      base::win::GetVersion() >= base::win::VERSION_WIN10
+          ? PROCESS_PER_MONITOR_DPI_AWARE
+          : PROCESS_SYSTEM_DPI_AWARE;
+  if (!SetProcessDpiAwarenessWrapper(process_dpi_awareness)) {
     SetProcessDPIAwareWrapper();
   }
 }