[Cocoa] DevTools: align devtools splitter to integer pixels to avoid half-pixel artifacts on HiDPI.

chrome/browser/ui/cocoa/dev_tools_controller.mm

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import "chrome/browser/ui/cocoa/dev_tools_controller.h"
 
 #include <algorithm>
 
 #include <Cocoa/Cocoa.h>
 
@@ skipping 199 matching lines @@
                ofSubviewAt:(NSInteger)dividerIndex {
   if ([splitView_ isVertical]) {
     return NSWidth([splitView_ frame]) - [splitView_ dividerThickness] -
         devToolsWindow_->GetMinimumWidth();
   } else {
     return NSHeight([splitView_ frame]) - [splitView_ dividerThickness] -
         devToolsWindow_->GetMinimumHeight();
   }
 }
 
+- (CGFloat)splitView:(NSSplitView *)splitView
+    constrainSplitPosition:(CGFloat)proposedPosition
+               ofSubviewAt:(NSInteger)dividerIndex {
+  return round(proposedPosition);
+}
+
 -(void)splitViewWillResizeSubviews:(NSNotification *)notification {
   [[splitView_ window] disableScreenUpdatesUntilFlush];
 }
 
 @end