overscroll: Enable overscroll navigation by default.

content/browser/web_contents/navigation_controller_impl.cc

 // Copyright (c) 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 "content/browser/web_contents/navigation_controller_impl.h"
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/file_util.h"
 #include "base/logging.h"
@@ skipping 461 matching lines @@
     return NULL;
 
   return entries_[index].get();
 }
 
 int NavigationControllerImpl::GetIndexForOffset(int offset) const {
   return GetCurrentEntryIndex() + offset;
 }
 
 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;
 
   NavigationEntryImpl* entry =
       NavigationEntryImpl::FromNavigationEntry(GetLastCommittedEntry());
   if (!entry)
     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;
 
   if (!take_screenshot_callback_.is_null())
     take_screenshot_callback_.Run(render_view_host);
 
   skia::PlatformBitmap* temp_bitmap = new skia::PlatformBitmap;
   render_view_host->CopyFromBackingStore(gfx::Rect(),
       view->GetViewBounds().size(),
@@ skipping 17 matching lines @@
       break;
     }
   }
 
   if (!entry) {
     LOG(ERROR) << "Invalid entry with unique id: " << unique_id;
     return;
   }
 
   if (!success) {
-    LOG(ERROR) << "Taking snapshot was unsuccessful for "
-               << unique_id;
     ClearScreenshot(entry);
     return;
   }
 
   std::vector<unsigned char> data;
   if (gfx::PNGCodec::EncodeBGRASkBitmap(bitmap->GetBitmap(), true, &data)) {
     if (!entry->screenshot())
       ++screenshot_count_;
     entry->SetScreenshotPNGData(data);
     PurgeScreenshotsIfNecessary();
@@ skipping 1225 matching lines @@
     const base::Callback<base::Time()>& get_timestamp_callback) {
   get_timestamp_callback_ = get_timestamp_callback;
 }
 
 void NavigationControllerImpl::SetTakeScreenshotCallbackForTest(
     const base::Callback<void(RenderViewHost*)>& take_screenshot_callback) {
   take_screenshot_callback_ = take_screenshot_callback;
 }
 
 }  // namespace content