Modify WebBluetooth chooser based on UI review feedback

chrome/browser/ui/cocoa/chooser_content_view_cocoa.mm

 // Copyright 2016 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/chooser_content_view_cocoa.h"
 
 #include <algorithm>
 
 #include "base/macros.h"
 #include "base/strings/sys_string_conversions.h"
@@ skipping 549 matching lines @@
 
     // Cancel button.
     CGFloat cancelButtonOriginX = kChooserWidth - kMarginX - cancelButtonWidth;
     CGFloat cancelButtonOriginY = connectButtonOriginY;
     [cancelButton_
         setFrameOrigin:NSMakePoint(cancelButtonOriginX, cancelButtonOriginY)];
     [self addSubview:cancelButton_];
 
     // Separator.
     CGFloat separatorOriginX = 0.0f;
-    CGFloat separatorOriginY = kMarginY + helpButtonHeight + kVerticalPadding;
-    [separator_ setFrameOrigin:NSMakePoint(separatorOriginX, separatorOriginY)];
+    separatorOriginY_ = kMarginY + helpButtonHeight + kVerticalPadding;
+    [separator_
+        setFrameOrigin:NSMakePoint(separatorOriginX, separatorOriginY_)];
     [self addSubview:separator_];
 
     // Help button.
     CGFloat helpButtonOriginX = kMarginX;
     CGFloat helpButtonOriginY = (kVerticalPadding + kMarginY) / 2;
     [helpButton_
         setFrameOrigin:NSMakePoint(helpButtonOriginX, helpButtonOriginY)];
     [helpButton_ setTarget:self];
     [helpButton_ setAction:@selector(onHelpPressed:)];
     [self addSubview:helpButton_];
@@ skipping 289 matching lines @@
       [tableView_ viewAtColumn:0 row:row makeIfNecessary:YES];
   return [tableRowView text];
 }
 
 - (NSTextField*)tableRowViewPairedStatus:(NSInteger)row {
   ChooserContentTableRowView* tableRowView =
       [tableView_ viewAtColumn:0 row:row makeIfNecessary:YES];
   return [tableRowView pairedStatus];
 }
 
+- (void)drawRect:(NSRect)rect {
+  [[NSColor colorWithCalibratedWhite:245.0f / 255.0f alpha:1.0f] setFill];
+  NSRect footnoteFrame =
+      NSMakeRect(0.0f, 0.0f, kChooserWidth, separatorOriginY_);
+  NSRectFill(footnoteFrame);
+  [super drawRect:footnoteFrame];
+}
+
 @end