Add HiDPI flag for Windows

ui/base/win/dpi.cc

 // Copyright (c) 2012 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 "ui/base/win/dpi.h"
 
 #include <windows.h>
-
+#include "base/command_line.h"
 #include "base/win/scoped_hdc.h"
 #include "ui/base/layout.h"
 #include "base/win/registry.h"
+#include "ui/base/ui_base_switches.h"
 #include "ui/gfx/display.h"
 #include "ui/gfx/point_conversions.h"
 #include "ui/gfx/rect_conversions.h"
 #include "ui/gfx/size_conversions.h"
 
 namespace {
 
 int kDefaultDPIX = 96;
 int kDefaultDPIY = 96;
 
+bool IsHighDPIEnabled() {
+  // Default is disabled.
+  if (CommandLine::ForCurrentProcess()->HasSwitch(switches::kHighDPISupport)) {
+    return CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
+        switches::kHighDPISupport).compare("1") == 0;
+  }
+  return false;
+}
+
 float GetDeviceScaleFactorImpl() {
 #if defined(ENABLE_HIDPI)
-  float scale = gfx::Display::HasForceDeviceScaleFactor() ?
-      gfx::Display::GetForcedDeviceScaleFactor() : ui::GetDPIScale();
-  // Quantize to nearest supported scale factor.
-  scale = ui::GetScaleFactorScale(ui::GetScaleFactorFromScale(scale));
-  return scale;
-#else
+  if (IsHighDPIEnabled()) {
+    float scale = gfx::Display::HasForceDeviceScaleFactor() ?
+        gfx::Display::GetForcedDeviceScaleFactor() : ui::GetDPIScale();
+    // Quantize to nearest supported scale factor.
+    scale = ui::GetScaleFactorScale(ui::GetScaleFactorFromScale(scale));
+    return scale;
+  }
+#endif
   return 1.0f;
-#endif
 }
 
 BOOL IsProcessDPIAwareWrapper() {
   typedef BOOL(WINAPI *IsProcessDPIAwarePtr)(VOID);
   IsProcessDPIAwarePtr is_process_dpi_aware_func =
       reinterpret_cast<IsProcessDPIAwarePtr>(
           GetProcAddress(GetModuleHandleA("user32.dll"), "IsProcessDPIAware"));
   if (is_process_dpi_aware_func)
     return is_process_dpi_aware_func();
   return FALSE;
@@ skipping 93 matching lines @@
         }
       }
     }
   }
   return scale;
 }
 
 }  // namespace win
 
 }  // namespace ui