Adds DevTools commands for forced viewport override.

content/renderer/devtools/render_widget_screen_metrics_emulator.cc

Index: content/renderer/devtools/render_widget_screen_metrics_emulator.cc
diff --git a/content/renderer/devtools/render_widget_screen_metrics_emulator.cc b/content/renderer/devtools/render_widget_screen_metrics_emulator.cc
index 6c27f46570fe8912622ec1d850abaa1db971bd0b..01b676c41f7200225d09c2de04b428a2b120d7ea 100644
--- a/content/renderer/devtools/render_widget_screen_metrics_emulator.cc
+++ b/content/renderer/devtools/render_widget_screen_metrics_emulator.cc
@@ -68,7 +68,7 @@ void RenderWidgetScreenMetricsEmulator::Apply() {
         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(