overscroll: Take a screenshot at more appropriate times.

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 f6f87d5a70448b3792a687d6b8264048281b4e40..150ff546a5cfae2a4d1983677ea9147ca86a9c03 100644
--- a/content/browser/web_contents/navigation_controller_impl.cc
+++ b/content/browser/web_contents/navigation_controller_impl.cc
@@ -493,6 +493,9 @@ void NavigationControllerImpl::TakeScreenshot() {
   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(),
@@ -753,12 +756,6 @@ void NavigationControllerImpl::DocumentLoadedInFrame() {
 bool NavigationControllerImpl::RendererDidNavigate(
     const ViewHostMsg_FrameNavigate_Params& params,
     LoadCommittedDetails* details) {
-  // When navigating away from the current page, take a screenshot of it in the
-  // current state so that it can be used during an overscroll-navigation
-  // gesture.
-  if (details->is_main_frame)
-    TakeScreenshot();
-
   // Save the previous state before we clobber it.
   if (GetLastCommittedEntry()) {
     details->previous_url = GetLastCommittedEntry()->GetURL();
@@ -1683,4 +1680,9 @@ void NavigationControllerImpl::SetGetTimestampCallbackForTest(
   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