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diff --git a/chrome/browser/cocoa/disclosure_view_controller.mm b/chrome/browser/cocoa/disclosure_view_controller.mm
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+++ b/chrome/browser/cocoa/disclosure_view_controller.mm
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+// 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/disclosure_view_controller.h"
+#include "base/logging.h"
+#include "base/scoped_nsobject.h"
+
+const NSCellStateValue kInitialDisclosureState = NSOffState;
+const NSInteger kClosedBoxHeight = 20;
+NSString* const kKVODisclosedKey = @"disclosed";
+
+// This class externalizes the state of the disclosure control.  When the
+// disclosure control is pressed it changes the state of this object.  In turn
+// the KVO machinery detects the change to |disclosed| and signals the
+// |observeValueForKeyPath| call in the |DisclosureViewController|.
+@interface DisclosureViewState : NSObject {
+ @private
+  NSCellStateValue disclosed;
+}
+@end
+
+@implementation DisclosureViewState
+@end
+
+@interface DisclosureViewController(PrivateMethods)
+
+- (void)initDisclosureState:(NSCellStateValue)state;
+- (NSRect)openStateFrameSize:(NSRect)startFrame;
+- (NSRect)closedStateFrameSize:(NSRect)startFrame;
+
+- (void)startAnimations:(NSView*)view
+                  start:(NSRect)startFrame
+                    end:(NSRect)endFrame;
+
+- (void)discloseDetails:(NSCellStateValue)state;
+
+- (void)observeValueForKeyPath:(NSString*)keyPath
+                      ofObject:(id)object
+                        change:(NSDictionary*)change
+                       context:(void*)context;
+
+@end
+
+@implementation DisclosureViewController
+
+@synthesize disclosureState = disclosureState_;
+
+- (void)awakeFromNib {
+  // Create the disclosure state.
+  [self setDisclosureState:[[[DisclosureViewState alloc] init] autorelease]];
+
+  // Set up the initial disclosure state before we install the observer.
+  // We don't want our animations firing before we're done initializing.
+  [disclosureState_ setValue:[NSNumber numberWithInt:kInitialDisclosureState]
+           forKey:kKVODisclosedKey];
+
+  // Pick up "open" height from the initial state of the view in the nib.
+  openHeight_ = [[self view] frame].size.height;
+
+  // Set frame size according to initial disclosure state.
+  [self initDisclosureState:kInitialDisclosureState];
+
+  // Setup observers so that when disclosure state changes we resize frame
+  // accordingly.
+  [disclosureState_ addObserver:self forKeyPath:kKVODisclosedKey
+             options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld
+             context:nil];
+}
+
+- (void)dealloc {
+  [disclosureState_ removeObserver:self forKeyPath:kKVODisclosedKey];
+  [disclosureState_ release];
+  [super dealloc];
+}
+
+@end
+
+@implementation DisclosureViewController(PrivateMethods)
+
+// Initializes the view's frame geometry based on the input |state|.
+// If the |state| is NSOnState then the frame size corresponds to "open".
+// If the |state| is NSOffState then the frame size corresponds to "closed".
+// The |origin.x| and |size.width| remain unchanged, but the |origin.y| and
+// |size.height| may vary.
+- (void)initDisclosureState:(NSCellStateValue)state {
+  if (state == NSOnState) {
+    [[self view] setFrame:[self openStateFrameSize:[[self view] frame]]];
+  }
+  else if (state == NSOffState) {
+    [[self view] setFrame:[self closedStateFrameSize:[[self view] frame]]];
+  }
+  else {
+    NOTREACHED();
+  }
+}
+
+// Computes the frame geometry during the "open" state of the disclosure view.
+- (NSRect)openStateFrameSize:(NSRect)startFrame {
+  return NSMakeRect(startFrame.origin.x,
+                    startFrame.size.height - openHeight_ +
+                        startFrame.origin.y,
+                    startFrame.size.width,
+                    openHeight_);
+}
+
+// Computes the frame geometry during the "closed" state of the disclosure view.
+- (NSRect)closedStateFrameSize:(NSRect)startFrame {
+  return NSMakeRect(startFrame.origin.x,
+                    startFrame.size.height - kClosedBoxHeight +
+                        startFrame.origin.y,
+                    startFrame.size.width,
+                    kClosedBoxHeight);
+}
+
+// Animates the opening or closing of the disclosure view.  The |startFrame|
+// specifies the frame geometry at the beginning of the animation and the
+// |endFrame| specifies the geometry at the end of the animation.  The input
+// |view| is view managed by this controller.
+- (void)startAnimations:(NSView*)view
+                  start:(NSRect)startFrame
+                    end:(NSRect)endFrame
+{
+  // Setup dictionary describing animation.
+  // Create the attributes dictionary for the first view.
+  NSMutableDictionary* dictionary;
+  dictionary = [NSDictionary dictionaryWithObjectsAndKeys:
+      // Specify which view to modify.
+      view, NSViewAnimationTargetKey,
+      // Specify the starting position of the view.
+      [NSValue valueWithRect:startFrame], NSViewAnimationStartFrameKey,
+      // Change the ending position of the view.
+      [NSValue valueWithRect:endFrame], NSViewAnimationEndFrameKey,
+      nil];
+
+  // Create the view animation object.
+  scoped_nsobject<NSViewAnimation> animation;
+  animation.reset([[NSViewAnimation alloc] initWithViewAnimations:
+               [NSArray arrayWithObject:dictionary]]);
+
+  // Set some additional attributes for the animation.
+  [animation.get() setDuration:.2];
+  [animation.get() setAnimationCurve:NSAnimationEaseIn];
+
+  // Run the animation.
+  [animation.get() startAnimation];
+}
+
+// This method is invoked when the disclosure state changes.  It computes
+// the appropriate view frame geometry and then initiates the animation to
+// change that geometry.
+- (void)discloseDetails:(NSCellStateValue)state {
+  NSRect startFrame = [[self view] frame];
+  NSRect endFrame = startFrame;
+
+  if (state == NSOnState) {
+    endFrame = [self openStateFrameSize:startFrame];
+  } else if (state == NSOffState) {
+    endFrame = [self closedStateFrameSize:startFrame];
+  } else {
+    NOTREACHED();
+    return;
+  }
+
+  [self startAnimations:[self view] start:startFrame end:endFrame];
+}
+
+// The |DisclosureViewController| is an observer of an instance of a
+// |DisclosureViewState| object.  This object lives within the controller's
+// nib file.  When the KVO machinery detects a change to the state
+// it triggers this call and we initiate the change in frame geometry of the
+// view.
+- (void)observeValueForKeyPath:(NSString*)keyPath
+                      ofObject:(id)object
+                        change:(NSDictionary*)change
+                       context:(void*)context {
+  if ([keyPath isEqualToString:kKVODisclosedKey]) {
+    NSCellStateValue newValue =
+        [[change objectForKey:NSKeyValueChangeNewKey] intValue];
+    NSCellStateValue oldValue =
+        [[change objectForKey:NSKeyValueChangeOldKey] intValue];
+
+    if (newValue != oldValue) {
+      [self discloseDetails:newValue];
+    }
+  }
+}
+
+@end