mac: Add overscroll animator slider

content/browser/web_contents/web_contents_view_overscroll_animator_mac.h

+// 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.
+
+#ifndef CONTENT_BROWSER_WEB_CONTENTS_WEB_CONTENTS_VIEW_OVERSCROLL_ANIMATOR_MAC_H_
+#define CONTENT_BROWSER_WEB_CONTENTS_WEB_CONTENTS_VIEW_OVERSCROLL_ANIMATOR_MAC_H_
+
+#import <Cocoa/Cocoa.h>
+
+namespace content {
+class WebContentsImpl;
+}
+
+// NSViews that intend to manage the animation associated with an overscroll
+// must implement this protocol.
+@protocol WebContentsOverscrollAnimator
+// Begin an overscroll animation to the left or the right.
+- (void)beginOverscrollLeft:(BOOL)left;

[Avi (use Gerrit), 2014/06/06 23:09:44]

I would much rather see a two-value enum.

[erikchen, 2014/06/07 00:34:03]

Done.

+
+// Some implementations require the WebContentsView to supply a snapshot of a
+// previous navigation state. The WebContentsView should call this method at the
+// beginning of an overscroll animation, and supply a snapshot if required.
+- (BOOL)needsNavigationSnapshot;
+
+// Supply a snapshot for use during the overscroll animation.
+- (void)supplyNavigationSnapshot:(NSImage*)image;

[Avi (use Gerrit), 2014/06/06 23:09:44]

I don't understand how this goes. Is the WebContentsView supposed to poll with
-needsNavigationSnapshot? This strikes me as a callback situation, where the
animator somehow asks, "hey, gimme a snapshot", rather than the WCV knowing that
it needs to ask.

[erikchen, 2014/06/07 00:34:03]

I've reworked the methods in question to clarify the situation. Starting an
overscroll now requires a direction and an NSImage. A single method
-needsNavigationSnapshot determines whether NSImage should be non-nil.

+
+// Due to the nature of some of the overscroll animations, implementators of
+// this protocol must have control over the layout of the RenderWidgetHost's
+// NativeView. When there is no overscroll animation in progress, the
+// implementor must guarantee that the frame of the RenderWidetHost's NativeView

[Avi (use Gerrit), 2014/06/06 23:09:44]

s/RenderWidetHost/RenderWidgetHost/

[erikchen, 2014/06/07 00:34:03]

Done.

+// in screen coordinates is the same as its own frame in screen coordinates.
+// Due to the odd ownership cycles of the RenderWidgetHost's NativeView, it is
+// important that its presence in the NSView hierarchy is the only strong
+// reference, and that when it gets removed from the NSView hierarchy, it will
+// be dealloc'ed shortly thereafter.
+- (void)addRenderWidgetHostNativeView:(NSView*)view;
+
+// During an overscroll animation, |progress| ranges from 0 to 2, and indicates
+// how close the overscroll is to completing. If the overscroll ends with
+// |progress| >= 1, then the overscroll is considered completed.

[Avi (use Gerrit), 2014/06/06 23:09:44]

These usually are 0-1 ranged. Why 0-2?

[erikchen, 2014/06/07 00:34:03]

I could keep progress from 0-1, and compare against "0.5", but I've got another
implementation of WebContentsOverscrollAnimator waiting in the wings which uses
the progress value differently. (It basically caps progress at 1, on a scale
from 0-2). 

In the context of both implementations of WebContentsOverscrollAnimator, 0-2
made more sense.

+- (void)updateOverscrollProgress:(CGFloat)progress;
+
+// Animate the finish of the overscroll and perform a navigation. The navigation
+// may not happen synchronously, but is guaranteed to eventually occur.
+- (void)completeOverscroll:(content::WebContentsImpl*)webContents;
+
+// Animate the cancellation of the overscroll.
+- (void)cancelOverscroll;
+@end
+
+#endif  // CONTENT_BROWSER_WEB_CONTENTS_WEB_CONTENTS_VIEW_OVERSCROLL_ANIMATOR_MAC_H_