overscroll: Enable overscroll navigation by default.

content/browser/web_contents/navigation_controller_impl.cc

Index: content/browser/web_contents/navigation_controller_impl.cc
diff --git a/content/browser/web_contents/navigation_controller_impl.cc b/content/browser/web_contents/navigation_controller_impl.cc
index e5b34b5e0dc5ed468af80f006b04ef9baa26cb70..a4ec35fb626b3b13b14125f0b7c86edc4d305d79 100644
--- a/content/browser/web_contents/navigation_controller_impl.cc
+++ b/content/browser/web_contents/navigation_controller_impl.cc
@@ -479,8 +479,8 @@ int NavigationControllerImpl::GetIndexForOffset(int offset) const {
 }
 
 void NavigationControllerImpl::TakeScreenshot() {
-  static bool overscroll_enabled = CommandLine::ForCurrentProcess()->
-      HasSwitch(switches::kEnableOverscrollHistoryNavigation);
+  static bool overscroll_enabled = !CommandLine::ForCurrentProcess()->
+      HasSwitch(switches::kDisableOverscrollHistoryNavigation);
   if (!overscroll_enabled)
     return;
 
@@ -490,6 +490,10 @@ void NavigationControllerImpl::TakeScreenshot() {
     return;
 
   RenderViewHost* render_view_host = web_contents_->GetRenderViewHost();
+  if (!static_cast<RenderViewHostImpl*>
+      (render_view_host)->overscroll_controller()) {
+    return;
+  }
   content::RenderWidgetHostView* view = render_view_host->GetView();
   if (!view)
     return;
@@ -527,8 +531,6 @@ void NavigationControllerImpl::OnScreenshotTaken(
   }
 
   if (!success) {
-    LOG(ERROR) << "Taking snapshot was unsuccessful for "
-               << unique_id;
     ClearScreenshot(entry);
     return;
   }