Replace subpixel font size heuristics with using OpenType gasp table

third_party/WebKit/Source/platform/fonts/win/FontPlatformDataWin.cpp

Index: third_party/WebKit/Source/platform/fonts/win/FontPlatformDataWin.cpp
diff --git a/third_party/WebKit/Source/platform/fonts/win/FontPlatformDataWin.cpp b/third_party/WebKit/Source/platform/fonts/win/FontPlatformDataWin.cpp
index 6031bf38b05555976f1377310ae0c2c59977bf90..e6bc30fe118526c6bd7c0c23756eadf3dee679ef 100644
--- a/third_party/WebKit/Source/platform/fonts/win/FontPlatformDataWin.cpp
+++ b/third_party/WebKit/Source/platform/fonts/win/FontPlatformDataWin.cpp
@@ -61,25 +61,16 @@ void FontPlatformData::setupPaint(SkPaint* paint, float, const Font*) const {
   if (ts <= kMaxSizeForEmbeddedBitmap)
     flags |= SkPaint::kEmbeddedBitmapText_Flag;
 
-  if (ts >= m_minSizeForAntiAlias) {
-    // 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.
-    if ((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;
-
-    SkASSERT(!(textFlags & ~textFlagsMask));
-    flags |= textFlags;
-  }
+  // Subpixel text positioning leads to uneven spacing without font

[eae, 2017/03/17 16:53:16]

This explanation is a little confusing at first as only describes a problem and
not the solution. How about starting with "Only use sub-pixel positioning if
anti aliasing is enabled."?

+  // smoothing. Subpixel test placement coordinates would be passed to Skia,
+  // which only has non-antialiased glyphs to draw, so they necessarily get
+  // clamped at pixel positions, which leads to uneven spacing, either too close
+  // or too far away from adjacent glyphs.
+  if (textFlags & SkPaint::kAntiAlias_Flag)
+    flags |= SkPaint::kSubpixelText_Flag;
+
+  SkASSERT(!(textFlags & ~textFlagsMask));
+  flags |= textFlags;
 
   paint->setFlags(flags);
 }