navigation: Retain a screenshot of the page before it unloads

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 9481ed69c3db1a195ad77c892530b855e293adf8..ace043c4ba84c2d6fac9b060ebd11067dfa95f1c 100644
--- a/content/browser/web_contents/navigation_controller_impl.cc
+++ b/content/browser/web_contents/navigation_controller_impl.cc
@@ -28,6 +28,8 @@
 #include "content/public/browser/navigation_details.h"
 #include "content/public/browser/notification_service.h"
 #include "content/public/browser/notification_types.h"
+#include "content/public/browser/render_widget_host.h"
+#include "content/public/browser/render_widget_host_view.h"
 #include "content/public/browser/storage_partition.h"
 #include "content/public/browser/user_metrics.h"
 #include "content/public/browser/web_contents_delegate.h"
@@ -37,6 +39,8 @@
 #include "net/base/escape.h"
 #include "net/base/mime_util.h"
 #include "net/base/net_util.h"
+#include "skia/ext/platform_canvas.h"
+#include "ui/gfx/codec/png_codec.h"
 #include "webkit/glue/glue_serialize.h"
 
 namespace content {
@@ -470,6 +474,50 @@ int NavigationControllerImpl::GetIndexForOffset(int offset) const {
   return GetCurrentEntryIndex() + offset;
 }
 
+void NavigationControllerImpl::TakeScreenshot() {
+  CHECK(web_contents_);
+
+  NavigationEntryImpl* active_entry =
+      NavigationEntryImpl::FromNavigationEntry(GetActiveEntry());
+  if (!active_entry)
+    return;
+
+  RenderViewHost* render_view_host = web_contents_->GetRenderViewHost();
+  content::RenderWidgetHostView* view = render_view_host->GetView();
+  if (!view)
+    return;
+
+  skia::PlatformBitmap* temp_bitmap = new skia::PlatformBitmap;
+  render_view_host->CopyFromBackingStore(gfx::Rect(),
+      view->GetViewBounds().size(),
+      base::Bind(&NavigationControllerImpl::TakingScreenshotComplete,
+                 base::Unretained(this),
+                 active_entry,
+                 base::Owned(temp_bitmap)),
+      temp_bitmap);
+}
+
+void NavigationControllerImpl::TakingScreenshotComplete(
+    NavigationEntryImpl* entry,
+    skia::PlatformBitmap* bitmap,
+    bool success) {
+  int index = GetIndexOfEntry(entry);
+  if (index < 0) {
+    LOG(ERROR) << "Invalid entry";
+    return;
+  }
+
+  if (!success) {
+    LOG(ERROR) << "Taking snapshot was unsuccessful for "
+               << entry->GetURL().spec();
+    return;
+  }
+
+  std::vector<unsigned char> data;
+  if (gfx::PNGCodec::EncodeBGRASkBitmap(bitmap->GetBitmap(), true, &data))
+    entry->SetScreenshotPNGData(data);
+}
+
 bool NavigationControllerImpl::CanGoBack() const {
   return entries_.size() > 1 && GetCurrentEntryIndex() > 0;
 }
@@ -690,6 +738,8 @@ void NavigationControllerImpl::DocumentLoadedInFrame() {
 bool NavigationControllerImpl::RendererDidNavigate(
     const ViewHostMsg_FrameNavigate_Params& params,
     LoadCommittedDetails* details) {
+  if (details->is_main_frame)
+    TakeScreenshot();
 
   // Save the previous state before we clobber it.
   if (GetLastCommittedEntry()) {
@@ -1441,6 +1491,8 @@ void NavigationControllerImpl::PruneOldestEntryIfFull() {
 void NavigationControllerImpl::NavigateToPendingEntry(ReloadType reload_type) {
   needs_reload_ = false;
 
+  TakeScreenshot();
+
   // If we were navigating to a slow-to-commit page, and the user performs
   // a session history navigation to the last committed page, RenderViewHost
   // will force the throbber to start, but WebKit will essentially ignore the