Make WebView work for external displays (over Presentations).

ui/snapshot/snapshot_android.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 "ui/snapshot/snapshot.h"
 
 #include "base/bind.h"
 #include "cc/output/copy_output_request.h"
 #include "third_party/skia/include/core/SkBitmap.h"
 #include "ui/android/view_android.h"
@@ skipping 21 matching lines @@
   return false;
 }
 
 static void MakeAsyncCopyRequest(
     gfx::NativeWindow window,
     const gfx::Rect& source_rect,
     const cc::CopyOutputRequest::CopyOutputRequestCallback& callback) {
   scoped_ptr<cc::CopyOutputRequest> request =
       cc::CopyOutputRequest::CreateBitmapRequest(callback);
 
-  const gfx::Display& display =
-      gfx::Screen::GetNativeScreen()->GetPrimaryDisplay();
-  float device_scale_factor = display.device_scale_factor();
+  float device_scale_factor =
+      gfx::Display::HasForceDeviceScaleFactor()
+          ? gfx::Display::GetForcedDeviceScaleFactor()

[jdduke (slow), 2015/07/15 16:03:07]

Why not use GetDisplayNearestWindow which should do the scale work for you?

[gsennton, 2015/07/15 19:26:21]

GetDisplayNearestWindow takes a NativeView (contrary to what the method name
suggests) while we only have access to a NativeWindow here. (And a ViewAndroid
holds a pointer to a WindowAndroid but not the other way around).

+          : window->GetDeviceDisplayInfo().GetDIPScale();
+
   gfx::Rect source_rect_in_pixel =
       gfx::ToEnclosingRect(gfx::ScaleRect(source_rect, device_scale_factor));
 
   // Account for the toolbar offset.
   gfx::Vector2dF offset = window->content_offset();
   gfx::Rect adjusted_source_rect(gfx::ToRoundedPoint(
       gfx::PointF(source_rect_in_pixel.x() + offset.x(),
                   source_rect_in_pixel.y() + offset.y())),
       source_rect_in_pixel.size());
 
@@ skipping 30 matching lines @@
 void GrabViewSnapshotAsync(
     gfx::NativeView view,
     const gfx::Rect& source_rect,
     scoped_refptr<base::TaskRunner> background_task_runner,
     const GrabWindowSnapshotAsyncPNGCallback& callback) {
   GrabWindowSnapshotAsync(
       view->GetWindowAndroid(), source_rect, background_task_runner, callback);
 }
 
 }  // namespace ui