Disable scrollbar snapback on desktop Linux (Reland)

content/renderer/webscrollbarbehavior_impl_aura.cc

Index: content/renderer/webscrollbarbehavior_impl_aura.cc
diff --git a/content/renderer/webscrollbarbehavior_impl_gtkoraura.cc b/content/renderer/webscrollbarbehavior_impl_aura.cc
similarity index 82%
rename from content/renderer/webscrollbarbehavior_impl_gtkoraura.cc
rename to content/renderer/webscrollbarbehavior_impl_aura.cc
index a07e1d47fd727d6ee9492fde8e625acd39fc1154..489684ec7e52d3b55ebb963097d915823b8bb9fe 100644
--- a/content/renderer/webscrollbarbehavior_impl_gtkoraura.cc
+++ b/content/renderer/webscrollbarbehavior_impl_aura.cc
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "content/renderer/webscrollbarbehavior_impl_gtkoraura.h"
+#include "content/renderer/webscrollbarbehavior_impl_aura.h"
 
 #include "build/build_config.h"
 #include "third_party/WebKit/public/platform/WebPoint.h"
@@ -26,6 +26,11 @@ bool WebScrollbarBehaviorImpl::shouldSnapBackToDragOrigin(
     const blink::WebPoint& eventPoint,
     const blink::WebRect& scrollbarRect,
     bool isHorizontal) {
+// Disable snapback on desktop Linux.  See crbug.com/567968 for context.

[Peter Kasting, 2016/11/08 02:59:13]

FWIW, I'd omit the bug link and simply summarize here in a sentence or two why
we shouldn't do that on Linux.  That will be clearer than trying to decipher
from a bug with lots of comments which parts are relevant "context", especially
when you haven't actually posted on that bug with your rationale (and our IM
discussions aren't captured there either).

[Tom (Use chromium acct), 2016/11/08 03:07:45]

Done.

+#if (defined(OS_LINUX) && !defined(OS_CHROMEOS))
+  return false;
+#endif
+
   // Constants used to figure the drag rect outside which we should snap the
   // scrollbar thumb back to its origin. These calculations are based on
   // observing the behavior of the MSVC8 main window scrollbar + some
@@ -47,16 +52,7 @@ bool WebScrollbarBehaviorImpl::shouldSnapBackToDragOrigin(
       (isHorizontal ? kOffEndMultiplier : kOffSideMultiplier) * -thickness,
       (isHorizontal ? kOffSideMultiplier : kOffEndMultiplier) * -thickness);
 
-  // On most platforms, we should snap iff the event is outside our calculated
-  // rect.  On Linux, however, we should not snap for events off the ends, but
-  // not the sides, of the rect.
-#if (defined(OS_LINUX) && !defined(OS_CHROMEOS))
-  return isHorizontal ?
-      (eventPoint.y < noSnapRect.y() || eventPoint.y >= noSnapRect.bottom()) :
-      (eventPoint.x < noSnapRect.x() || eventPoint.x >= noSnapRect.right());
-#else
   return !noSnapRect.Contains(eventPoint);
-#endif
 }
 
 }  // namespace content