Use plus/minus 0.5 instead of 1 when calculating zoomed length.

Source/core/rendering/style/RenderStyle.h

Index: Source/core/rendering/style/RenderStyle.h
diff --git a/Source/core/rendering/style/RenderStyle.h b/Source/core/rendering/style/RenderStyle.h
index eb5496ea25990b2a81140b143f74c47db208e030..0c943f32ae86d8837694cbaec4031a7be6d17566 100644
--- a/Source/core/rendering/style/RenderStyle.h
+++ b/Source/core/rendering/style/RenderStyle.h
@@ -1788,19 +1788,22 @@ private:
     unsigned computeChangedContextSensitiveProperties(const RenderStyle& other, StyleDifference) const;
 };
 
+// FIXME: Reduce/remove the dependency on zoom adjusted int values.
+// The float or LayoutUnit versions of layout values should be used.
 inline int adjustForAbsoluteZoom(int value, float zoomFactor)
 {
     if (zoomFactor == 1)
         return value;
     // Needed because computeLengthInt truncates (rather than rounds) when scaling up.
+    float fvalue = value;
     if (zoomFactor > 1) {
         if (value < 0)
-            value--;
+            fvalue -= 0.5f;
         else
-            value++;
+            fvalue += 0.5f;
     }
 
-    return roundForImpreciseConversion<int>(value / zoomFactor);
+    return roundForImpreciseConversion<int>(fvalue / zoomFactor);
 }
 
 inline int adjustForAbsoluteZoom(int value, const RenderStyle* style)