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

content/renderer/gpu/render_widget_compositor.cc

Index: content/renderer/gpu/render_widget_compositor.cc
diff --git a/content/renderer/gpu/render_widget_compositor.cc b/content/renderer/gpu/render_widget_compositor.cc
index c684a3726600f88c53f1746928f0cb2334ecfa1e..7ca7e226b06e0637602e7d8945ee33884349300b 100644
--- a/content/renderer/gpu/render_widget_compositor.cc
+++ b/content/renderer/gpu/render_widget_compositor.cc
@@ -621,7 +621,10 @@ WebFloatPoint RenderWidgetCompositor::adjustEventPointForPinchZoom(
 }
 
 void RenderWidgetCompositor::setDeviceScaleFactor(float device_scale) {
-  layer_tree_host_->SetDeviceScaleFactor(device_scale);
+  if (IsUseZoomForDSFEnabled())
+    layer_tree_host_->SetPaintedDeviceScaleFactor(device_scale);

[danakj, 2015/10/22 23:15:29]

I think maybe you want a separate function in RWC and blink will call one or the
other

[oshima, 2015/10/23 18:05:36]

This is called from mulitple places, 

RenderWidgetFullscreenPepper
WebFrameWidgetImpl
WeebPagePopupImpl
WebViewImpl

and I felt this is a bit cleaner, especially the old path will be removed once
migration is done. I'll wait for the owners' suggestion.

[piman, 2015/10/23 19:30:33]

I kinda agree with Dana. WebViewImpl (and others) know what they are doing and
should tell RWC how to render / pass metadata, instead of RWC second-guessing
what they intend to do based on the flag (seems like a bit of a layering
violation).

[enne (OOO), 2015/10/23 21:21:25]

Agreed here as well.

[oshima, 2015/10/23 22:05:02]

How about letting WebWidgetClient set the device scale instead? I wanted Blink
not to know the mode. I think the way I changed WebViewImpl was mistake. I
should instead have had a method like WebViewImpl::setZoomFactorForDSF, and
remove enableUseZoomXxxx (I updated this part). This way, we can restrict the
mode knowledge in RenderWidget/RenderViewImpl.

What do you think?

[oshima, 2015/10/30 17:35:38]

This change wasn't actually necessary. I changed the following

* Add SetPaintedDeviceScaleFactor on RWC
* Let RenderViewImpl call RWC::SetPaintedDeviceScaleFactor. This is enough
because blink's dsf won't change.

I also removed the WebWidgetClient::deviceScaleFactor as it isn't necessary.

+  else
+    layer_tree_host_->SetDeviceScaleFactor(device_scale);
 }
 
 void RenderWidgetCompositor::setBackgroundColor(blink::WebColor color) {