Fix darkly-drawn Show All button in Downloads Shelf.

chrome/browser/ui/cocoa/download/download_show_all_button.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/download/download_show_all_button.h"
 
 #include "base/logging.h"
 #import "chrome/browser/ui/cocoa/download/download_show_all_cell.h"
 #import "chrome/browser/ui/cocoa/view_id_util.h"
 #include "grit/theme_resources.h"
@@ skipping 26 matching lines @@
 }
 
 - (BOOL)isOpaque {
   // Make this control opaque so that sub-pixel anti-aliasing works when
   // CoreAnimation is enabled.
   return YES;
 }
 
 - (void)drawRect:(NSRect)rect {
   NSView* downloadShelfView = [self ancestorWithViewID:VIEW_ID_DOWNLOAD_SHELF];
-  [self cr_drawUsingAncestor:downloadShelfView inRect:rect];
+  // Previously the show all button used cr_drawUsingAncestor:inRect: to use
+  // the download shelf to draw its background. However when the download
+  // shelf has zero height, the shelf's drawing methods don't work as expected
+  // because they constrain their drawing to the shelf's bounds rect. This
+  // situation occurs sometimes when the shelf is about to become visible,
+  // and the result is a very dark show all button
+  //
+  // To work around this problem, we'll call a variant of that method which
+  // does restrict drawing to the ancestor view's bounds.
+  [self cr_drawUsingAncestor:downloadShelfView
+                      inRect:rect
+     clippedToAncestorBounds:NO];
   [super drawRect:rect];
 }
 
 // ThemedWindowDrawing implementation.
 
 - (void)windowDidChangeTheme {
   [self setNeedsDisplay:YES];
 }
 
 - (void)windowDidChangeActive {
   [self setNeedsDisplay:YES];
 }
 
 @end