Disable overscroll on Windows machines w/o touchscreen

chrome/browser/ui/browser.cc

Index: chrome/browser/ui/browser.cc
diff --git a/chrome/browser/ui/browser.cc b/chrome/browser/ui/browser.cc
index 63c0e8c8fe2c1c5fe51228ad5318f7b250ad5e9d..3d7d9b3a6898bdee755630abed313809e7f6ce5b 100644
--- a/chrome/browser/ui/browser.cc
+++ b/chrome/browser/ui/browser.cc
@@ -191,6 +191,7 @@
 #include "net/url_request/url_request_context.h"
 #include "third_party/WebKit/public/web/WebWindowFeatures.h"
 #include "ui/base/l10n/l10n_util.h"
+#include "ui/base/touch/touch_device.h"

[sadrul, 2014/09/30 16:32:15]

Add this include below for OS_WIN in line ~200?

[mfomitchev, 2014/09/30 18:30:33]

Done.

 #include "ui/base/window_open_disposition.h"
 #include "ui/gfx/point.h"
 #include "ui/shell_dialogs/selected_file_info.h"
@@ -1127,7 +1128,22 @@ void Browser::TabStripEmpty() {
 }
 
 bool Browser::CanOverscrollContent() const {
-#if defined(USE_AURA)
+#if defined(USE_AURA) && 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 allowOverscroll = ui::IsTouchDevicePresent();

[sadrul, 2014/09/30 16:32:15]

allow_overscroll

Also, AURA is always turned on for Windows, so just

#if defined(OS_WIN)
..
#elif defined(USE_AURA)
..
#else
..
#endif

or

#if defined(USE_AURA)
#if defined(OS_WIN)
...
#else
...
#endif
...
#endif

[mfomitchev, 2014/09/30 18:30:33]

Done.

+#elif defined(USE_AURA)
+  bool allowOverscroll = true;
+#else
+  bool allowOverscroll = false;
+#endif
+
+  if (!allowOverscroll)
+    return false;
+
   const std::string value = CommandLine::ForCurrentProcess()->
       GetSwitchValueASCII(switches::kOverscrollHistoryNavigation);
   bool overscroll_enabled = value != "0";
@@ -1143,9 +1159,6 @@ bool Browser::CanOverscrollContent() const {
   if (value == "1" && bookmark_bar_state_ == BookmarkBar::DETACHED)
     return false;
   return true;
-#else
-  return false;
-#endif
 }
 
 bool Browser::ShouldPreserveAbortedURLs(WebContents* source) {