Disable overscroll on Windows machines w/o touchscreen

chrome/browser/ui/browser.cc

 // Copyright 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.
 
 #include "chrome/browser/ui/browser.h"
 
 #if defined(OS_WIN)
 #include <windows.h>
 #include <shellapi.h>
 #endif  // defined(OS_WIN)
@@ skipping 183 matching lines @@
 #include "ui/base/window_open_disposition.h"
 #include "ui/gfx/point.h"
 #include "ui/shell_dialogs/selected_file_info.h"
 
 #if defined(OS_WIN)
 #include "base/win/metro.h"
 #include "chrome/browser/ssl/ssl_error_info.h"
 #include "chrome/browser/task_manager/task_manager.h"
 #include "chrome/browser/ui/view_ids.h"
 #include "components/autofill/core/browser/autofill_ie_toolbar_import_win.h"
+#include "ui/base/touch/touch_device.h"
 #include "ui/base/win/shell.h"
 #endif  // OS_WIN
 
 #if defined(OS_CHROMEOS)
 #include "chrome/browser/chromeos/drive/file_system_util.h"
 #endif
 
 #if defined(USE_ASH)
 #include "ash/ash_switches.h"
 #endif
@@ skipping 906 matching lines @@
   //       still present.
   base::MessageLoop::current()->PostTask(
       FROM_HERE, base::Bind(&Browser::CloseFrame, weak_factory_.GetWeakPtr()));
 
   // Instant may have visible WebContents that need to be detached before the
   // window system closes.
   instant_controller_.reset();
 }
 
 bool Browser::CanOverscrollContent() const {
 #if defined(USE_AURA)

[sky, 2014/09/30 21:46:05]

Oy, this is hard to read with all the ifdefs. How about a
IsOverscrollEnabledOnPlatform? You could even put the win implementation in
browser_win.

[mfomitchev, 2014/09/30 22:32:29]

Hmm.. how can I put the win implementation into browser_win if I also have a
more generic implementation in browser.cc? There's no separate BrowserWin
class... I guess I could have two separate implementations for aura and non-aura
in browser.cc (rather than one implementation for both) - is this what you want?
I'd still need an ifdef for OS_WIN in the aura implementation, since Windows
uses Aura.

+#if defined(OS_WIN)
+  // Don't enable overscroll on Windows machines unless they have a touch
+  // screen as these machines typically don't have a touchpad capable of
+  // horizontal scrolling. We are purposefully biased towards "no" here,
+  // so that we don't waste resources capturing screenshots for horizontal
+  // overscroll navigation unnecessarily.
+  bool allow_overscroll = ui::IsTouchDevicePresent();
+#else
+  bool allow_overscroll = true;
+#endif
+#else
+  bool allow_overscroll = false;
+#endif
+
+  if (!allow_overscroll)
+    return false;
+
   const std::string value = CommandLine::ForCurrentProcess()->
       GetSwitchValueASCII(switches::kOverscrollHistoryNavigation);
   bool overscroll_enabled = value != "0";
   if (!overscroll_enabled)
     return false;
   if (is_app() || is_devtools() || !is_type_tabbed())
     return false;
 
   // The detached bookmark bar has appearance of floating above the
   // web-contents. This does not play nicely with overscroll navigation
   // gestures. So disable overscroll navigation when the bookmark bar is in the
   // detached state and the overscroll effect moves the layers.
   if (value == "1" && bookmark_bar_state_ == BookmarkBar::DETACHED)
     return false;
   return true;
-#else
-  return false;
-#endif
 }
 
 bool Browser::ShouldPreserveAbortedURLs(WebContents* source) {
   // Allow failed URLs to stick around in the omnibox on the NTP, but not when
   // other pages have committed.
   Profile* profile = Profile::FromBrowserContext(source->GetBrowserContext());
   if (!profile || !source->GetController().GetLastCommittedEntry())
     return false;
   GURL committed_url(source->GetController().GetLastCommittedEntry()->GetURL());
   return chrome::IsNTPURL(committed_url, profile);
@@ skipping 1317 matching lines @@
   if (contents && !allow_js_access) {
     contents->web_contents()->GetController().LoadURL(
         target_url,
         content::Referrer(),
         ui::PAGE_TRANSITION_LINK,
         std::string());  // No extra headers.
   }
 
   return contents != NULL;
 }