Fixing GestureNav on HDPI displays.

The GestireNav screenshot dimensions are density-independent, because when we capture the screenshot we scale it to RVH's bounds: https://code.google.com/p/chromium/codesearch#chromium/src/content/browser/frame_host/navigation_entry_screenshot_manager.cc&q=navigation_entry_sc&sq=package:chromium&type=cs&l=136

Thus we don't need to scale it again when we paint during the overscroll gesture.

BUG=402280

Review URL: https://codereview.chromium.org/507083002

Cr-Commit-Position: refs/heads/master@{#292426}

content/browser/web_contents/aura/overscroll_navigation_overlay.cc

@@ -200,8 +200,7 @@ ui::Layer* OverscrollNavigationOverlay::CreateSlideLayer(int offset) {
   gfx::Image image;
   if (entry && entry->screenshot().get()) {
     std::vector<gfx::ImagePNGRep> image_reps;
-    image_reps.push_back(gfx::ImagePNGRep(entry->screenshot(),
-        ui::GetScaleFactorForNativeView(window_.get())));
+    image_reps.push_back(gfx::ImagePNGRep(entry->screenshot(), 1.0f));
     image = gfx::Image(image_reps);
   }
   if (!layer_delegate_)

content/browser/web_contents/web_contents_view_aura.cc

@@ -134,8 +134,7 @@ class OverscrollWindowDelegate : public ImageWindowDelegate {
     gfx::Image image;
     if (entry && entry->screenshot().get()) {
       std::vector<gfx::ImagePNGRep> image_reps;
-      image_reps.push_back(gfx::ImagePNGRep(entry->screenshot(),
-          ui::GetScaleFactorForNativeView(web_contents_window())));
+      image_reps.push_back(gfx::ImagePNGRep(entry->screenshot(), 1.0f));
       image = gfx::Image(image_reps);
     }
     SetImage(image);