[DevTools] Handle emulated device scale factor and original device scale factor properly.

third_party/WebKit/Source/web/WebViewImpl.cpp

 /*
  * Copyright (C) 2011, 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 392 matching lines @@
     , m_chromeClientImpl(ChromeClientImpl::create(this))
     , m_contextMenuClientImpl(this)
     , m_dragClientImpl(this)
     , m_editorClientImpl(this)
     , m_spellCheckerClientImpl(this)
     , m_storageClientImpl(this)
     , m_shouldAutoResize(false)
     , m_zoomLevel(0)
     , m_minimumZoomLevel(zoomFactorToZoomLevel(minTextSizeMultiplier))
     , m_maximumZoomLevel(zoomFactorToZoomLevel(maxTextSizeMultiplier))
-    , m_zoomFactorForDeviceScaleFactor(1.f)
+    , m_zoomFactorForDeviceScaleFactor(0.f)
     , m_maximumLegibleScale(1)
     , m_doubleTapZoomPageScaleFactor(0)
     , m_doubleTapZoomPending(false)
     , m_enableFakePageScaleAnimationForTesting(false)
     , m_fakePageScaleAnimationPageScaleFactor(0)
     , m_fakePageScaleAnimationUseAnchor(false)
     , m_doingDragAndDrop(false)
     , m_ignoreInputEvents(false)
     , m_compositorDeviceScaleFactorOverride(0)
     , m_rootLayerScale(1)
@@ skipping 2624 matching lines @@
         m_zoomLevel = zoomLevel;
 
     // TODO(nasko): Setting zoom level needs to be refactored to support
     // out-of-process iframes. See https://crbug.com/528407.
     if (mainFrame()->isWebRemoteFrame())
         return m_zoomLevel;
 
     LocalFrame* frame = mainFrameImpl()->frame();
     if (!WebLocalFrameImpl::pluginContainerFromFrame(frame)) {
         float zoomFactor = m_zoomFactorOverride ? m_zoomFactorOverride : static_cast<float>(zoomLevelToZoomFactor(m_zoomLevel));
-        zoomFactor *= m_zoomFactorForDeviceScaleFactor;
+        if (m_zoomFactorForDeviceScaleFactor) {
+            if (m_compositorDeviceScaleFactorOverride) {
+                // Adjust the page's DSF so that DevicePixelRatio becomes m_zoomFactorForDeviceScaleFactor.
+                page()->setDeviceScaleFactor(m_zoomFactorForDeviceScaleFactor / m_compositorDeviceScaleFactorOverride);
+                zoomFactor *= m_compositorDeviceScaleFactorOverride;
+            } else {
+                page()->setDeviceScaleFactor(1.f);
+                zoomFactor *= m_zoomFactorForDeviceScaleFactor;
+            }
+        }
         frame->setPageZoomFactor(zoomFactor);
     }
 
     return m_zoomLevel;
 }
 
 void WebViewImpl::zoomLimitsChanged(double minimumZoomLevel,
                                     double maximumZoomLevel)
 {
     m_minimumZoomLevel = minimumZoomLevel;
@@ skipping 696 matching lines @@
 unsigned long WebViewImpl::createUniqueIdentifierForRequest()
 {
     return createUniqueIdentifier();
 }
 
 void WebViewImpl::setCompositorDeviceScaleFactorOverride(float deviceScaleFactor)
 {
     if (m_compositorDeviceScaleFactorOverride == deviceScaleFactor)
         return;
     m_compositorDeviceScaleFactorOverride = deviceScaleFactor;
+    if (m_zoomFactorForDeviceScaleFactor) {
+        setZoomLevel(zoomLevel());
+        return;
+    }
     if (page() && m_layerTreeView)
         updateLayerTreeDeviceScaleFactor();
 }
 
 void WebViewImpl::setRootLayerTransform(const WebSize& rootLayerOffset, float rootLayerScale)
 {
     if (m_rootLayerScale == rootLayerScale && m_rootLayerOffset == rootLayerOffset)
         return;
     m_rootLayerScale = rootLayerScale;
     m_rootLayerOffset = rootLayerOffset;
@@ skipping 789 matching lines @@
 {
     // TODO(oshima): Investigate if this should return the ScreenInfo's scale factor rather than
     // page's scale factor, which can be 1 in use-zoom-for-dsf mode.
     if (!page())
         return 1;
 
     return page()->deviceScaleFactor();
 }
 
 } // namespace blink