mac: Make dynamic DPI changes work.

content/renderer/render_widget.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 "content/renderer/render_widget.h"
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/debug/trace_event.h"
 #include "base/logging.h"
@@ skipping 1472 matching lines @@
   if (is_accelerated_compositing_active_) {
     webwidget_->setNeedsRedraw();
     scheduleComposite();
   } else {
     gfx::Rect repaint_rect(size_to_paint.width(), size_to_paint.height());
     didInvalidateRect(repaint_rect);
   }
 }
 
 void RenderWidget::OnSetDeviceScaleFactor(float device_scale_factor) {
-  // TODO(thakis): Set device_scale_factor_, possibly trigger a repaint.
+  if (device_scale_factor_ == device_scale_factor)
+    return;
+
+  device_scale_factor_ = device_scale_factor;
+
+  if (!is_accelerated_compositing_active_) {
+    didInvalidateRect(gfx::Rect(size_.width(), size_.height()));
+  } else {
+    scheduleComposite();
+  }
 }
 
 void RenderWidget::OnSetTextDirection(WebTextDirection direction) {
   if (!webwidget_)
     return;
   webwidget_->setTextDirection(direction);
 }
 
 webkit::ppapi::PluginInstance* RenderWidget::GetBitmapForOptimizedPluginPaint(
     const gfx::Rect& paint_bounds,
@@ skipping 239 matching lines @@
   }
 }
 
 bool RenderWidget::WillHandleMouseEvent(const WebKit::WebMouseEvent& event) {
   return false;
 }
 
 bool RenderWidget::WebWidgetHandlesCompositorScheduling() const {
   return false;
 }