[DirectWrite] Set blink device scale factor

Change renderer_main_platform_delegate_win to set the device scale
factor for the renderer in PlatformInitialize. The blink text rendering
code requires on this value being set.

Depends on Blink change https://codereview.chromium.org/553163002/
which must land and roll before this can be landed.

R=cpu@chromium.org, creis@chromium.org

Review URL: https://codereview.chromium.org/561503002

Cr-Commit-Position: refs/heads/master@{#294397}

content/renderer/renderer_main_platform_delegate_win.cc

@@ -25,6 +25,7 @@
 #include "third_party/icu/source/i18n/unicode/timezone.h"
 #include "third_party/skia/include/ports/SkFontMgr.h"
 #include "third_party/skia/include/ports/SkTypeface_win.h"
+#include "ui/gfx/win/dpi.h"
 
 #ifdef ENABLE_VTUNE_JIT_INTERFACE
 #include "v8/src/third_party/vtune/v8-vtune.h"
@@ -106,6 +107,7 @@ void RendererMainPlatformDelegate::PlatformInitialize() {
     }
   }
   blink::WebFontRendering::setUseDirectWrite(use_direct_write);
+  blink::WebFontRendering::setDeviceScaleFactor(gfx::GetDPIScale());
   if (use_direct_write) {
     blink::WebRuntimeFeatures::enableSubpixelFontScaling(true);
   }