Mac: Fix theme image drawing when building with >=10.9 SDK.

chrome/browser/ui/cocoa/tabs/tab_strip_background_view.mm

+// Copyright 2014 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/tabs/tab_strip_background_view.h"
+
+#import "chrome/browser/ui/cocoa/framed_browser_window.h"
+#import "ui/base/cocoa/nsview_additions.h"
+
+@implementation TabStripBackgroundView
+
+- (void)drawRect:(NSRect)dirtyRect {
+  // Only the top corners are rounded. For simplicity, round all 4 corners but
+  // draw the bottom corners outside of the visible bounds.
+  float cornerRadius = 4.0;
+  NSRect roundedRect = [self bounds];
+  roundedRect.origin.y -= cornerRadius;
+  roundedRect.size.height += cornerRadius;
+  [[NSBezierPath bezierPathWithRoundedRect:roundedRect
+                                   xRadius:cornerRadius
+                                   yRadius:cornerRadius] addClip];
+  BOOL themed = [FramedBrowserWindow drawWindowThemeInDirtyRect:dirtyRect
+                                                        forView:self
+                                                         bounds:roundedRect
+                                           forceBlackBackground:NO];
+  // Pinstripe the top.
+  if (themed) {
+    CGFloat lineWidth = [self cr_lineWidth];
+    NSRect strokeRect = NSInsetRect(roundedRect, -lineWidth/2, lineWidth/2);

[erikchen, 2014/09/27 00:23:33]

I see that this logic is just copied from framed_browser_window, but why would
we ever want to align on the half pixel? 

[Andre, 2014/09/27 18:17:02]

A path's stroke is drawn right on the line instead of inside or outside the
line.
So in this case where the line is a round integer, a 1px width stroke will be
drawn 0.5px inside and 0.5 outside the path.
The vertical lines are moved 0.5px inside so that the top line gets a full
pixel. The horizontal lines are moved 0.5px outside so that it's not visible,
but to still get the rounded corners to get a border.

[Andre, 2014/09/27 18:47:00]

Uploaded a new patch to add this as comment.

+    NSBezierPath* path = [NSBezierPath bezierPathWithRoundedRect:strokeRect
+                                                         xRadius:cornerRadius
+                                                         yRadius:cornerRadius];
+    [path setLineWidth:lineWidth];
+    [[NSColor colorWithCalibratedWhite:1.0 alpha:0.5] set];
+    [path stroke];
+  }
+}
+
+- (void)viewWillMoveToWindow:(NSWindow*)window {
+  if ([self window]) {
+    [[NSNotificationCenter defaultCenter]
+        removeObserver:self
+                  name:NSWindowDidBecomeMainNotification
+                object:[self window]];
+    [[NSNotificationCenter defaultCenter]
+        removeObserver:self
+                  name:NSWindowDidResignMainNotification
+                object:[self window]];
+  }
+  if (window) {
+    [[NSNotificationCenter defaultCenter]
+        addObserver:self
+           selector:@selector(windowFocusDidChange:)
+               name:NSWindowDidBecomeMainNotification
+             object:window];
+    [[NSNotificationCenter defaultCenter]
+        addObserver:self
+           selector:@selector(windowFocusDidChange:)
+               name:NSWindowDidResignMainNotification
+             object:window];
+  }
+}
+
+- (void)windowFocusDidChange:(NSNotification*)notification {
+  // The theme image may depend on the window's active state.
+  [self setNeedsDisplay:YES];
+}
+
+@end