Make sure line widths in the range of 0px and 1px are rounded up to 1px for visibility.

third_party/WebKit/Source/core/css/resolver/AnimatedStyleBuilder.cpp

 /*
  * Copyright (C) 2013 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.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 81 matching lines @@
     ASSERT(toAnimatableUnknown(value)->toCSSValueID() == CSSValueAuto);
     return Length(Auto);
 }
 
 template<typename T> T animatableValueClampTo(const AnimatableValue* value, T min = defaultMinimumForClamp<T>(), T max = defaultMaximumForClamp<T>())
 {
     static_assert(WTF::IsInteger<T>::value, "should use integral type T when rounding values");
     return clampTo<T>(roundForImpreciseConversion<T>(toAnimatableDouble(value)->toDouble()), min, max);
 }
 
+template<typename T> T animatableLineWidthClamp(const AnimatableValue* value)
+{
+    double doubleValue = toAnimatableDouble(value)->toDouble();
+    // This matches StyleBuilderConverter::convertLineWidth().
+    return (doubleValue > 0 && doubleValue < 1) ? 1 : animatableValueClampTo<T>(value);
+}
+
 LengthBox animatableValueToLengthBox(const AnimatableValue* value, const StyleResolverState& state, ValueRange range = ValueRangeAll)
 {
     const AnimatableLengthBox* animatableLengthBox = toAnimatableLengthBox(value);
     return LengthBox(
         animatableValueToLength(animatableLengthBox->top(), state, range),
         animatableValueToLength(animatableLengthBox->right(), state, range),
         animatableValueToLength(animatableLengthBox->bottom(), state, range),
         animatableValueToLength(animatableLengthBox->left(), state, range));
 }
 
@@ skipping 196 matching lines @@
         style->setBorderBottomColor(toAnimatableColor(value)->color());
         style->setVisitedLinkBorderBottomColor(toAnimatableColor(value)->visitedLinkColor());
         return;
     case CSSPropertyBorderBottomLeftRadius:
         style->setBorderBottomLeftRadius(animatableValueToLengthSize(value, state, ValueRangeNonNegative));
         return;
     case CSSPropertyBorderBottomRightRadius:
         style->setBorderBottomRightRadius(animatableValueToLengthSize(value, state, ValueRangeNonNegative));
         return;
     case CSSPropertyBorderBottomWidth:
-        style->setBorderBottomWidth(animatableValueClampTo<unsigned>(value));
+        style->setBorderBottomWidth(animatableLineWidthClamp<unsigned>(value));
         return;
     case CSSPropertyBorderImageOutset:
         style->setBorderImageOutset(animatableValueToBorderImageLengthBox(value, state));
         return;
     case CSSPropertyBorderImageSlice:
         style->setBorderImageSlices(animatableValueToLengthBox(toAnimatableLengthBoxAndBool(value)->box(), state, ValueRangeNonNegative));
         style->setBorderImageSlicesFill(toAnimatableLengthBoxAndBool(value)->flag());
         return;
     case CSSPropertyBorderImageSource:
         style->setBorderImageSource(state.styleImage(property, *toAnimatableImage(value)->toCSSValue()));
         return;
     case CSSPropertyBorderImageWidth:
         style->setBorderImageWidth(animatableValueToBorderImageLengthBox(value, state));
         return;
     case CSSPropertyBorderLeftColor:
         style->setBorderLeftColor(toAnimatableColor(value)->color());
         style->setVisitedLinkBorderLeftColor(toAnimatableColor(value)->visitedLinkColor());
         return;
     case CSSPropertyBorderLeftWidth:
-        style->setBorderLeftWidth(animatableValueClampTo<unsigned>(value));
+        style->setBorderLeftWidth(animatableLineWidthClamp<unsigned>(value));
         return;
     case CSSPropertyBorderRightColor:
         style->setBorderRightColor(toAnimatableColor(value)->color());
         style->setVisitedLinkBorderRightColor(toAnimatableColor(value)->visitedLinkColor());
         return;
     case CSSPropertyBorderRightWidth:
-        style->setBorderRightWidth(animatableValueClampTo<unsigned>(value));
+        style->setBorderRightWidth(animatableLineWidthClamp<unsigned>(value));
         return;
     case CSSPropertyBorderTopColor:
         style->setBorderTopColor(toAnimatableColor(value)->color());
         style->setVisitedLinkBorderTopColor(toAnimatableColor(value)->visitedLinkColor());
         return;
     case CSSPropertyBorderTopLeftRadius:
         style->setBorderTopLeftRadius(animatableValueToLengthSize(value, state, ValueRangeNonNegative));
         return;
     case CSSPropertyBorderTopRightRadius:
         style->setBorderTopRightRadius(animatableValueToLengthSize(value, state, ValueRangeNonNegative));
         return;
     case CSSPropertyBorderTopWidth:
-        style->setBorderTopWidth(animatableValueClampTo<unsigned>(value));
+        style->setBorderTopWidth(animatableLineWidthClamp<unsigned>(value));
         return;
     case CSSPropertyBottom:
         style->setBottom(animatableValueToLength(value, state));
         return;
     case CSSPropertyBoxShadow:
         style->setBoxShadow(toAnimatableShadow(value)->shadowList());
         return;
     case CSSPropertyClip:
         style->setClip(animatableValueToLengthBox(value, state));
         return;
@@ skipping 94 matching lines @@
         style->setOrphans(clampTo<unsigned short>(round(toAnimatableDouble(value)->toDouble()), 1));
         return;
     case CSSPropertyOutlineColor:
         style->setOutlineColor(toAnimatableColor(value)->color());
         style->setVisitedLinkOutlineColor(toAnimatableColor(value)->visitedLinkColor());
         return;
     case CSSPropertyOutlineOffset:
         style->setOutlineOffset(animatableValueClampTo<int>(value));
         return;
     case CSSPropertyOutlineWidth:
-        style->setOutlineWidth(animatableValueClampTo<unsigned short>(value));
+        style->setOutlineWidth(animatableLineWidthClamp<unsigned short>(value));
         return;
     case CSSPropertyPaddingBottom:
         style->setPaddingBottom(animatableValueToLength(value, state, ValueRangeNonNegative));
         return;
     case CSSPropertyPaddingLeft:
         style->setPaddingLeft(animatableValueToLength(value, state, ValueRangeNonNegative));
         return;
     case CSSPropertyPaddingRight:
         style->setPaddingRight(animatableValueToLength(value, state, ValueRangeNonNegative));
         return;
@@ skipping 60 matching lines @@
         style->setColumnGap(clampTo(toAnimatableDouble(value)->toDouble(), 0));
         return;
     case CSSPropertyWebkitColumnRuleColor:
         style->setColumnRuleColor(toAnimatableColor(value)->color());
         style->setVisitedLinkColumnRuleColor(toAnimatableColor(value)->visitedLinkColor());
         return;
     case CSSPropertyWebkitColumnWidth:
         style->setColumnWidth(clampTo(toAnimatableDouble(value)->toDouble(), std::numeric_limits<float>::epsilon()));
         return;
     case CSSPropertyWebkitColumnRuleWidth:
-        style->setColumnRuleWidth(clampTo<unsigned short>(toAnimatableDouble(value)->toDouble()));
+        style->setColumnRuleWidth(animatableLineWidthClamp<unsigned short>(value));
         return;
     case CSSPropertyWebkitFilter:
         style->setFilter(toAnimatableFilterOperations(value)->operations());
         return;
     case CSSPropertyBackdropFilter:
         style->setBackdropFilter(toAnimatableFilterOperations(value)->operations());
         return;
     case CSSPropertyWebkitMaskBoxImageOutset:
         style->setMaskBoxImageOutset(animatableValueToBorderImageLengthBox(value, state));
         return;
@@ skipping 129 matching lines @@
     case CSSPropertyRy:
         style->setRy(animatableValueToLength(value, state, ValueRangeNonNegative));
         return;
 
     default:
         ASSERT_NOT_REACHED();
     }
 }
 
 } // namespace blink