Don't round x-axis for text runs when subpixel font scaling is enabled

Source/core/rendering/InlineTextBox.cpp

Index: Source/core/rendering/InlineTextBox.cpp
diff --git a/Source/core/rendering/InlineTextBox.cpp b/Source/core/rendering/InlineTextBox.cpp
index fee393d6e8be5d6c59974f98f8dbd361831c32f4..f3d870f2b8be0932869c7ab01ed1cb91c57f6d36 100644
--- a/Source/core/rendering/InlineTextBox.cpp
+++ b/Source/core/rendering/InlineTextBox.cpp
@@ -478,7 +478,13 @@ void InlineTextBox::paint(PaintInfo& paintInfo, const LayoutPoint& paintOffset,
     LayoutUnit paintEnd = isHorizontal() ? paintInfo.rect.maxX() : paintInfo.rect.maxY();
     LayoutUnit paintStart = isHorizontal() ? paintInfo.rect.x() : paintInfo.rect.y();
 
-    LayoutPoint adjustedPaintOffset = roundedIntPoint(paintOffset);
+    // When subpixel font scaling is enabled text runs are positioned at
+    // subpixel boundaries on the x-axis and thus there is no reason to
+    // snap the x value. We still round the y-axis to ensure consistent
+    // line heights.
+    LayoutPoint adjustedPaintOffset = RuntimeEnabledFeatures::subpixelFontScalingEnabled()
+        ? LayoutPoint(paintOffset.x(), paintOffset.y().round())
+        : roundedIntPoint(paintOffset);
 
     if (logicalStart >= paintEnd || logicalStart + logicalExtent <= paintStart)
         return;
@@ -517,7 +523,6 @@ void InlineTextBox::paint(PaintInfo& paintInfo, const LayoutPoint& paintOffset,
     adjustedPaintOffset.move(0, styleToUse->isHorizontalWritingMode() ? 0 : -logicalHeight());
 
     FloatPoint boxOrigin = locationIncludingFlipping();
-    // FIXME: Shouldn't these offsets be rounded?
     boxOrigin.move(adjustedPaintOffset.x().toFloat(), adjustedPaintOffset.y().toFloat());
     FloatRect boxRect(boxOrigin, LayoutSize(logicalWidth(), logicalHeight()));