Fix the mobile emulator to use the correct device scale when disabled.

The mobile emulator was triggering a layout before it had reapplied the
original viewport parameters when it was being disabled, which with
use-zoom-for-dsf enabled was causing the wrong viewport size to be given
to various components, like plugins and scrollbars.

BUG=628501,628185

Review-Url: https://codereview.chromium.org/2168313002
Cr-Commit-Position: refs/heads/master@{#407294}

content/renderer/devtools/render_widget_screen_metrics_emulator.cc

@@ -25,10 +25,10 @@ RenderWidgetScreenMetricsEmulator::RenderWidgetScreenMetricsEmulator(
 }
 
 RenderWidgetScreenMetricsEmulator::~RenderWidgetScreenMetricsEmulator() {
+  delegate_->Resize(original_resize_params_);
   delegate_->SetScreenMetricsEmulationParameters(false, emulation_params_);
   delegate_->SetScreenRects(original_view_screen_rect_,
                             original_window_screen_rect_);
-  delegate_->Resize(original_resize_params_);
 }
 
 void RenderWidgetScreenMetricsEmulator::ChangeEmulationParams(