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..e45efbb1e9f27fb04746317b9accfb7ecd2554e9 100644
--- a/Source/core/rendering/style/RenderStyle.h
+++ b/Source/core/rendering/style/RenderStyle.h
@@ -1793,14 +1793,15 @@ 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)