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

content/renderer/render_view_impl.cc

Index: content/renderer/render_view_impl.cc
diff --git a/content/renderer/render_view_impl.cc b/content/renderer/render_view_impl.cc
index 584854c2f1c4724dff935a339d77194352d91e79..dadfdbb01e7af1096b7033b329c3f4a4e530c848 100644
--- a/content/renderer/render_view_impl.cc
+++ b/content/renderer/render_view_impl.cc
@@ -38,6 +38,7 @@
 #include "content/child/v8_value_converter_impl.h"
 #include "content/child/webmessageportchannel_impl.h"
 #include "content/common/content_constants_internal.h"
+#include "content/common/content_switches_internal.h"
 #include "content/common/database_messages.h"
 #include "content/common/dom_storage/dom_storage_types.h"
 #include "content/common/drag_messages.h"
@@ -745,8 +746,7 @@ void RenderViewImpl::Initialize(const ViewMsg_New_Params& params,
   // completing initialization.  Otherwise, we can finish it now.
   if (opener_id_ == MSG_ROUTING_NONE)
     did_show_ = true;
-
-  webview()->setDeviceScaleFactor(device_scale_factor_);
+  UpdateDeviceScaleFactor();
   webview()->setDisplayMode(display_mode_);
   webview()->settings()->setPreferCompositingToLCDTextEnabled(
       PreferCompositingToLCDText(compositor_deps_, device_scale_factor_));
@@ -3195,7 +3195,7 @@ void RenderViewImpl::OnImeConfirmComposition(
 void RenderViewImpl::SetDeviceScaleFactor(float device_scale_factor) {
   RenderWidget::SetDeviceScaleFactor(device_scale_factor);
   if (webview()) {
-    webview()->setDeviceScaleFactor(device_scale_factor);
+    UpdateDeviceScaleFactor();
     webview()->settings()->setPreferCompositingToLCDTextEnabled(
         PreferCompositingToLCDText(compositor_deps_, device_scale_factor_));
   }
@@ -3703,4 +3703,14 @@ void RenderViewImpl::DidStopLoadingIcons() {
   SendUpdateFaviconURL(urls);
 }
 
+void RenderViewImpl::UpdateDeviceScaleFactor() {
+  if (IsUseZoomForDSFEnabled()) {
+    compositor_->SetPaintedDeviceScaleFactor(device_scale_factor_);

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

side note: this is probably good enough for now, but I suspect later you'll want
to do this one at the RenderWidget level, for popups etc. consistency.

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

Acknowledged. I removed the dcheck in RWC becasue it's indeed called for popup.
I'll deal with it in a separate CL.

+    webview()->setZoomFactorForDeviceScaleFactor(
+        device_scale_factor_);
+  } else {
+    webview()->setDeviceScaleFactor(device_scale_factor_);
+  }
+}
+
 }  // namespace content