Adds DevTools commands for forced viewport override.

content/renderer/devtools/render_widget_screen_metrics_emulator.cc

 // Copyright 2016 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 "content/renderer/devtools/render_widget_screen_metrics_emulator.h"
 
 #include "content/common/resize_params.h"
 #include "content/public/common/context_menu_params.h"
 #include "content/renderer/devtools/render_widget_screen_metrics_emulator_delegate.h"
 
@@ skipping 50 matching lines @@
     scale_ = 1.f / ratio;
 
     // Center emulated view inside available view space.
     offset_.set_x(
         (original_size().width() - scale_ * applied_widget_rect_.width()) / 2);
     offset_.set_y(
         (original_size().height() - scale_ * applied_widget_rect_.height()) /
         2);
   } else {
     scale_ = emulation_params_.scale;
-    offset_.SetPoint(emulation_params_.offset.x, emulation_params_.offset.y);
+    offset_.SetPoint(0, 0);
     if (!emulation_params_.viewSize.width &&
         !emulation_params_.viewSize.height && scale_) {
       applied_widget_rect_.set_size(
           gfx::ScaleToRoundedSize(original_size(), 1.f / scale_));
     }
   }
 
   gfx::Rect window_screen_rect;
   if (emulation_params_.screenPosition ==
       blink::WebDeviceEmulationParams::Desktop) {
@@ skipping 109 matching lines @@
 
 gfx::Rect RenderWidgetScreenMetricsEmulator::AdjustValidationMessageAnchor(
     const gfx::Rect& anchor) {
   gfx::Rect scaled = gfx::ScaleToEnclosedRect(anchor, scale_);
   scaled.set_x(scaled.x() + offset_.x());
   scaled.set_y(scaled.y() + offset_.y());
   return scaled;
 }
 
 }  // namespace content