Introduce painted-device-scale-factor and use it when --enable-use-zoom-for-dsf is specified.

third_party/WebKit/Source/web/WebViewImpl.cpp

Index: third_party/WebKit/Source/web/WebViewImpl.cpp
diff --git a/third_party/WebKit/Source/web/WebViewImpl.cpp b/third_party/WebKit/Source/web/WebViewImpl.cpp
index fe889d4f9fb92f8fe078d49f546d9d80a5e741bc..be19f6e366d3b3151c69131c3b1c023cb8457f53 100644
--- a/third_party/WebKit/Source/web/WebViewImpl.cpp
+++ b/third_party/WebKit/Source/web/WebViewImpl.cpp
@@ -412,6 +412,7 @@ WebViewImpl::WebViewImpl(WebViewClient* client)
     , m_zoomLevel(0)
     , m_minimumZoomLevel(zoomFactorToZoomLevel(minTextSizeMultiplier))
     , m_maximumZoomLevel(zoomFactorToZoomLevel(maxTextSizeMultiplier))
+    , m_zoomFactorForDeviceScaleFactor(1.f)
     , m_maximumLegibleScale(1)
     , m_doubleTapZoomPageScaleFactor(0)
     , m_doubleTapZoomPending(false)
@@ -2958,6 +2959,7 @@ double WebViewImpl::setZoomLevel(double zoomLevel)
     LocalFrame* frame = mainFrameImpl()->frame();
     if (!WebLocalFrameImpl::pluginContainerFromFrame(frame)) {
         float zoomFactor = m_zoomFactorOverride ? m_zoomFactorOverride : static_cast<float>(zoomLevelToZoomFactor(m_zoomLevel));
+        zoomFactor *= m_zoomFactorForDeviceScaleFactor;
         frame->setPageZoomFactor(zoomFactor);
     }
 
@@ -3103,6 +3105,14 @@ void WebViewImpl::setDeviceScaleFactor(float scaleFactor)
         updateLayerTreeDeviceScaleFactor();
 }
 
+void WebViewImpl::setZoomFactorForDeviceScaleFactor(float zoomFactorForDeviceScaleFactor)
+{
+    if (!m_layerTreeView || m_zoomFactorForDeviceScaleFactor == zoomFactorForDeviceScaleFactor)
+        return;
+    m_zoomFactorForDeviceScaleFactor = zoomFactorForDeviceScaleFactor;

[piman, 2015/10/30 21:32:02]

ISTM you want to save the zoomFactorForDSF regardless of whether the
layerTreeView is initialized yet or not.

[oshima, 2015/10/30 23:23:12]

Done.

I also remove the equality check so that it updates zoom level if the call
didn't update zoom level.

+    setZoomLevel(m_zoomLevel);
+}
+
 void WebViewImpl::setDeviceColorProfile(const WebVector<char>& colorProfile)
 {
     if (!page())