[DirectWrite] Limit noSubpixelForSmallSizeFont to low-DPI

Source/platform/fonts/win/FontPlatformDataWin.cpp

 /*
  * Copyright (C) 2006, 2007 Apple Computer, Inc.
  * Copyright (c) 2006, 2007, 2008, 2009, 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 46 matching lines @@
     static const uint32_t textFlagsMask = SkPaint::kAntiAlias_Flag |
         SkPaint::kLCDRenderText_Flag |
         SkPaint::kGenA8FromLCD_Flag;
     flags &= ~textFlagsMask;
 
     if (ts <= kMaxSizeForEmbeddedBitmap)
         flags |= SkPaint::kEmbeddedBitmapText_Flag;
 
     if (ts >= m_minSizeForAntiAlias) {
 
-        // Subpixel text positioning looks pretty bad without font smoothing.
-        // Disable it unless some type of font smoothing is used. As most tests
-        // run without font smoothing we enable it for tests to ensure we get
-        // good test coverage matching the more common smoothing enabled
-        // behavior.
-        if (m_useSubpixelPositioning && ts >= m_minSizeForSubpixel
-            && ((textFlags & SkPaint::kAntiAlias_Flag) || LayoutTestSupport::isRunningLayoutTest()))
+        if (m_useSubpixelPositioning
+            // Disable subpixel text for certain older fonts at smaller sizes as
+            // they tend to get quite blurry at non-integer sizes and positions.
+            // For high-DPI this workaround isn't required.
+            && (ts >= m_minSizeForSubpixel
+                || FontCache::fontCache()->deviceScaleFactor() >= 1.5)
+
+            // Subpixel text positioning looks pretty bad without font
+            // smoothing. Disable it unless some type of font smoothing is used.
+            // As most tests run without font smoothing we enable it for tests
+            // to ensure we get good test coverage matching the more common
+            // smoothing enabled behavior.
+            && ((textFlags & SkPaint::kAntiAlias_Flag)
+                || LayoutTestSupport::isRunningLayoutTest()))
             flags |= SkPaint::kSubpixelText_Flag;
 
         // Only set painting flags when we're actually painting.
         if (context && !context->couldUseLCDRenderedText()) {
             textFlags &= ~SkPaint::kLCDRenderText_Flag;
             // If we *just* clear our request for LCD, then GDI seems to
             // sometimes give us AA text, and sometimes give us BW text. Since the
             // original intent was LCD, we want to force AA (rather than BW), so we
             // add a special bit to tell Skia to do its best to avoid the BW: by
             // drawing LCD offscreen and downsampling that to AA.
@@ skipping 68 matching lines @@
 {
     m_paintTextFlags = computePaintTextFlags(fontFamilyName());
 }
 
 bool FontPlatformData::defaultUseSubpixelPositioning()
 {
     return FontCache::fontCache()->useSubpixelPositioning();
 }
 
 } // namespace blink