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

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 6bdb139501906ac31f7a596d3822d692cc97bea6..2c3d6565405f5cfa435ec579bdc4fb41e6ee0d57 100644
--- a/third_party/WebKit/Source/web/WebViewImpl.cpp
+++ b/third_party/WebKit/Source/web/WebViewImpl.cpp
@@ -410,7 +410,7 @@ WebViewImpl::WebViewImpl(WebViewClient* client)
     , 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)
@@ -3055,7 +3055,15 @@ 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;
+        if (m_zoomFactorForDeviceScaleFactor) {
+          if (m_compositorDeviceScaleFactorOverride) {

[dgozman, 2016/03/02 01:19:56]

style: 4 spaces in blink

[oshima, 2016/03/02 03:15:07]

Done.

+            page()->setDeviceScaleFactor(m_zoomFactorForDeviceScaleFactor / m_compositorDeviceScaleFactorOverride);

[dgozman, 2016/03/02 01:19:56]

This is surprising. I thought in new mode device_scale_factor would always be
one. This makes emulation conceptually different from the regular case, which
I'd like to avoid.
Also, do you plan to remove device scale factor from page eventually? This would
block it.

[oshima, 2016/03/02 03:15:07]

DPR (Device Pixel Ratio), which emulator sets, is different from Device Scale
Factor.

DPR is computed by "Device Scale Factor set in Page" * ZoomFactor.

In new mode, compositor's device scale factor is always one, and instead it'll
apply zoom factor to blink side.
The above is to get the produce DPR in new mode. This behaves exactly same as
old mode.

And my new test should cover both new and old mode. (ChromeOS runs with new
mode, while other platforms runs with old mode)

Once the migration is completed, we should simply have "emulated DPR", which
does not take zoom factor into account.

+            zoomFactor *= m_compositorDeviceScaleFactorOverride;
+          } else {
+            page()->setDeviceScaleFactor(1.f);
+            zoomFactor *= m_zoomFactorForDeviceScaleFactor;
+          }
+        }
         frame->setPageZoomFactor(zoomFactor);
     }
 
@@ -3772,6 +3780,10 @@ void WebViewImpl::setCompositorDeviceScaleFactorOverride(float deviceScaleFactor
     if (m_compositorDeviceScaleFactorOverride == deviceScaleFactor)
         return;
     m_compositorDeviceScaleFactorOverride = deviceScaleFactor;
+    if (m_zoomFactorForDeviceScaleFactor) {
+        setZoomLevel(zoomLevel());
+        return;
+    }
     if (page() && m_layerTreeView)
         updateLayerTreeDeviceScaleFactor();
 }