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

BUG=270055

Review URL: https://chromiumcodereview.appspot.com/22630011

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@217110 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/ui/cocoa/dev_tools_controller.mm

@@ -217,6 +217,12 @@ using content::WebContents;
   }
 }
 
+- (CGFloat)splitView:(NSSplitView *)splitView
+    constrainSplitPosition:(CGFloat)proposedPosition
+               ofSubviewAt:(NSInteger)dividerIndex {
+  return round(proposedPosition);
+}
+
 -(void)splitViewWillResizeSubviews:(NSNotification *)notification {
   [[splitView_ window] disableScreenUpdatesUntilFlush];
 }