Fixed fractional border width on iOS

Summary:
Incorrect render for borders that are not proportional to device pixel: borders get stretched and become significantly bigger than expected.
Rdar: http://www.openradar.me/15959788

Incorrect render for borders that are not proportional to device pixel: borders get stretched and become significantly bigger than expected.
Rdar: http://www.openradar.me/15959788

Reviewed By: shergin

Differential Revision: D6317674

fbshipit-source-id: 6bc331447458583a02c0e56d0d011a31d31d70a8

Author: Nikita2k

React/Views/RCTBorderDrawing.m

@@ -59,6 +59,15 @@ RCTCornerInsets RCTGetCornerInsets(RCTCornerRadii cornerRadii,
   };
 }
 
+static UIEdgeInsets RCTRoundInsetsToPixel(UIEdgeInsets edgeInsets) {
+    edgeInsets.top = RCTRoundPixelValue(edgeInsets.top);
+    edgeInsets.bottom = RCTRoundPixelValue(edgeInsets.bottom);
+    edgeInsets.left = RCTRoundPixelValue(edgeInsets.left);
+    edgeInsets.right = RCTRoundPixelValue(edgeInsets.right);
+
+    return edgeInsets;
+}
+
 static void RCTPathAddEllipticArc(CGMutablePathRef path,
                                   const CGAffineTransform *m,
                                   CGPoint origin,
@@ -195,6 +204,11 @@ static CGContextRef RCTUIGraphicsBeginImageContext(CGSize size, CGColorRef backg
   const BOOL hasCornerRadii = RCTCornerRadiiAreAboveThreshold(cornerRadii);
   const RCTCornerInsets cornerInsets = RCTGetCornerInsets(cornerRadii, borderInsets);
 
+  // Incorrect render for borders that are not proportional to device pixel: borders get stretched and become
+  // significantly bigger than expected.
+  // Rdar: http://www.openradar.me/15959788
+  borderInsets = RCTRoundInsetsToPixel(borderInsets);
+
   const BOOL makeStretchable =
   (borderInsets.left + cornerInsets.topLeft.width +
    borderInsets.right + cornerInsets.bottomRight.width <= viewSize.width) &&