Change snasphotting API to take in a bounds Rect

chrome/browser/ui/window_snapshot/window_snapshot_mac.mm

 // Copyright (c) 2011 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.
 
 #include "chrome/browser/ui/window_snapshot/window_snapshot.h"
 
 #import <Cocoa/Cocoa.h>
 
 #include "base/logging.h"
 #include "base/mac/scoped_cftyperef.h"
 #include "base/memory/scoped_nsobject.h"
 #include "ui/gfx/rect.h"
 
 namespace browser {
 
 gfx::Rect GrabWindowSnapshot(gfx::NativeWindow window,
-    std::vector<unsigned char>* png_representation) {
+    std::vector<unsigned char>* png_representation,
+    gfx::Rect snapshot_bounds) {
   png_representation->clear();
 
+  CGRect windowRect = CGRectNUll;
+  if (!snapshot_bounds.IsEmpty()) {
+      gfx::Rect window_bounds = gfx::Rect([window frame]);
+      snapshot_bounds.Offset(window_bounds.left(), window_bounds.top());
+      windowRect = snapshot_bounds.ToCGRect();
+      DCHECK(snapshot_bounds.right() <= window_bounds.right());
+      DCHECK(snapshot_bounds.bottom() <= window_bounds.bottom()); 
+  }
+
   // Make sure to grab the "window frame" view so we get current tab +
   // tabstrip.
   NSView* view = [[window contentView] superview];
   base::mac::ScopedCFTypeRef<CGImageRef> windowSnapshot(CGWindowListCreateImage(
       CGRectNull, kCGWindowListOptionIncludingWindow,
       [[view window] windowNumber], kCGWindowImageBoundsIgnoreFraming));
   if (CGImageGetWidth(windowSnapshot) <= 0)
     return gfx::Rect();
 
   scoped_nsobject<NSBitmapImageRep> rep(
       [[NSBitmapImageRep alloc] initWithCGImage:windowSnapshot]);
   NSData* data = [rep representationUsingType:NSPNGFileType properties:nil];
   const unsigned char* buf = static_cast<const unsigned char*>([data bytes]);
   NSUInteger length = [data length];
   if (buf == NULL || length == 0)
     return gfx::Rect();
 
   png_representation->assign(buf, buf + length);
   DCHECK(!png_representation->empty());
 
   return gfx::Rect(static_cast<int>([rep pixelsWide]),
                    static_cast<int>([rep pixelsHigh]));
 }
 
 }  // namespace browser