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..1746ade6d2ae48fc91084da9b29fd1722b4b21f6 100644
--- a/chrome/browser/ui/browser.cc
+++ b/chrome/browser/ui/browser.cc
@@ -201,6 +201,7 @@
 #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
 
@@ -1128,6 +1129,23 @@ void Browser::TabStripEmpty() {
 
 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";
@@ -1143,9 +1161,6 @@ 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) {