Disable subpixel positioning if DirectWrite isn't initialized

ui/gfx/font_render_params_win.cc

Index: ui/gfx/font_render_params_win.cc
diff --git a/ui/gfx/font_render_params_win.cc b/ui/gfx/font_render_params_win.cc
index 354d1b248b740e13dfa9e7a815af73f47c6abd9b..3b1c247b9b22b1dc761dcd5346c33bbb47797860 100644
--- a/ui/gfx/font_render_params_win.cc
+++ b/ui/gfx/font_render_params_win.cc
@@ -6,6 +6,7 @@
 
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/singleton.h"
+#include "ui/gfx/win/direct_write.h"
 #include "ui/gfx/win/singleton_hwnd.h"
 
 namespace gfx {
@@ -34,7 +35,7 @@ class CachedFontRenderParams : public gfx::SingletonHwnd::Observer {
     BOOL enabled = false;
     if (SystemParametersInfo(SPI_GETFONTSMOOTHING, 0, &enabled, 0) && enabled) {
       params_->antialiasing = true;
-      params_->subpixel_positioning = true;
+      params_->subpixel_positioning = win::IsDirectWriteEnabled();

[msw, 2014/12/10 23:55:50]

Is this correct, or should we simply not round the run widths for RTHB + GDI?
https://code.google.com/p/chromium/codesearch#chromium/src/ui/gfx/render_text...
Please add a comment here, if this is needed, to explain its reasoning.

[ckocagil, 2014/12/11 01:07:11]

Rounding in RTHB and letting Skia do the rounding gives different results. When
we round in RTHB, we always start glyphs at integers. I remember trying both,
and ours giving visually better results as well as matching the native behavior.

I don't think we need a comment here though. DirectWrite supports subpixel
positioning, GDI does not. Whether we round ourselves or let Skia do it isn't a
concern here.

[msw, 2014/12/11 23:30:12]

Optionally: // GDI does not support subpixel positioning.

[ckocagil, 2014/12/12 09:52:11]

Done.

 
       UINT type = 0;
       if (SystemParametersInfo(SPI_GETFONTSMOOTHINGTYPE, 0, &type, 0) &&