Vertical scrolling arrows in bookmark bar folder windows when needed....

chrome/browser/cocoa/bookmark_bar_folder_window.mm

 // Copyright (c) 2010 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/cocoa/bookmark_bar_folder_window.h"
 
 #import "base/logging.h"
+#include "base/nsimage_cache_mac.h"
 #import "base/scoped_nsobject.h"
 #import "chrome/browser/cocoa/bookmark_bar_folder_controller.h"
 #import "third_party/GTM/AppKit/GTMNSColor+Luminance.h"
 #import "third_party/GTM/AppKit/GTMNSBezierPath+RoundRect.h"
 
 
 @implementation BookmarkBarFolderWindow
 
 - (id)initWithContentRect:(NSRect)contentRect
                 styleMask:(NSUInteger)windowStyle
@@ skipping 13 matching lines @@
 
 
 namespace {
 // Corner radius for our bookmark bar folder window.
 // Copied from bubble_view.mm.
 const CGFloat kViewCornerRadius = 4.0;
 }
 
 @implementation BookmarkBarFolderWindowContentView
 
+- (void)awakeFromNib {
+  arrowUpImage_.reset([nsimage_cache::ImageNamed(@"menu_overflow_up.pdf")
+                                    retain]);
+  arrowDownImage_.reset([nsimage_cache::ImageNamed(@"menu_overflow_down.pdf")
+                                      retain]);
+}
+
+// Draw the arrows at the top and bottom of the folder window as a
+// visual indication that scrolling is possible.  We always draw the
+// scrolling arrows; when not relevant (e.g. when not scrollable), the
+// scroll view overlaps me and the arrows aren't visible.
+- (void)drawScrollArrows:(NSRect)rect {
+  NSRect visibleRect = [self bounds];
+
+  // On top
+  [arrowUpImage_ setFlipped:[self isFlipped]];
+  NSRect imageRect = NSZeroRect;
+  imageRect.size = [arrowUpImage_ size];
+  NSRect drawRect = NSOffsetRect(
+      imageRect,
+      (NSWidth(visibleRect) - NSWidth(imageRect)) / 2,
+      NSHeight(visibleRect) - NSHeight(imageRect));
+  [arrowUpImage_ drawInRect:drawRect
+                   fromRect:imageRect
+                  operation:NSCompositeSourceOver
+                   fraction:1.0];
+
+  // On bottom
+  [arrowDownImage_ setFlipped:[self isFlipped]];
+  imageRect = NSZeroRect;
+  imageRect.size = [arrowDownImage_ size];
+  drawRect = NSOffsetRect(imageRect,
+                          (NSWidth(visibleRect) - NSWidth(imageRect)) / 2,
+                          0);
+  [arrowDownImage_ drawInRect:drawRect
+                     fromRect:imageRect
+                    operation:NSCompositeSourceOver
+                     fraction:1.0];
+}
+
 - (void)drawRect:(NSRect)rect {
   NSRect bounds = [self bounds];
   // Like NSMenus, only the bottom corners are rounded.
   NSBezierPath* bezier =
       [NSBezierPath gtm_bezierPathWithRoundRect:bounds
                             topLeftCornerRadius:0
                            topRightCornerRadius:0
                          bottomLeftCornerRadius:kViewCornerRadius
                         bottomRightCornerRadius:kViewCornerRadius];
   [bezier closePath];
@@ skipping 13 matching lines @@
       [base_color gtm_colorAdjustedFor:GTMColorationLightPenumbra
                                  faded:YES];
 
   scoped_nsobject<NSGradient> gradient(
     [[NSGradient alloc] initWithColorsAndLocations:startColor, 0.0,
                         midColor, 0.25,
                         endColor, 0.5,
                         glowColor, 0.75,
                         nil]);
   [gradient drawInBezierPath:bezier angle:0.0];
+
+  [self drawScrollArrows:rect];
 }
 
 @end
 
 
 @implementation BookmarkBarFolderWindowScrollView
 
 // We want "draw background" of the NSScrollView in the xib to be NOT
 // checked.  That allows us to round the bottom corners of the folder
 // window.  However that also allows some scrollWheel: events to leak
 // into the NSWindow behind it (even in a different application).
 // Better to plug the scroll leak than to round corners for M5.
 - (void)scrollWheel:(NSEvent *)theEvent {
   DCHECK([[[self window] windowController]
            respondsToSelector:@selector(scrollWheel:)]);
   [[[self window] windowController] scrollWheel:theEvent];
 }
 
-
 @end