Plugin Power Saver: Implement srcset syntax for posters.

components/plugins/renderer/webview_plugin.cc

Index: components/plugins/renderer/webview_plugin.cc
diff --git a/components/plugins/renderer/webview_plugin.cc b/components/plugins/renderer/webview_plugin.cc
index d14e4f7235af237575e186fd9f3bf07dfcedc347..ce65a0b87c0447e481d8645e7ad43b22cfe7679c 100644
--- a/components/plugins/renderer/webview_plugin.cc
+++ b/components/plugins/renderer/webview_plugin.cc
@@ -109,8 +109,13 @@ WebPluginContainer* WebViewPlugin::container() const { return container_; }
 
 bool WebViewPlugin::initialize(WebPluginContainer* container) {
   container_ = container;
-  if (container_)
+  if (container_) {
     old_title_ = container_->element().getAttribute("title");
+
+    // Propagate device scale to inner webview to load the correct resource
+    // when images have a "srcset" attribute.
+    web_view_->setDeviceScaleFactor(container_->deviceScaleFactor());
+  }
   return true;
 }
 
@@ -139,9 +144,17 @@ void WebViewPlugin::paint(WebCanvas* canvas, const WebRect& rect) {
   canvas->translate(SkIntToScalar(rect_.x()), SkIntToScalar(rect_.y()));
   canvas->save();
 
+  // Before actually painting, remove device scaling, as it would otherwise
+  // be applied twice.
+  web_view_->setDeviceScaleFactor(1);

[jbroman, 2015/03/06 20:25:49]

Changing the device scale factor of the page like this seems wrong (if nothing
else, it forces a style recalc).

Rather, I would think applying a scale by 1/dsf to the canvas (to counter the
one in blink::PageWidgetDelegate::paint) is reasonable.

(In my ideal world, it would be the caller of WebViewImpl::paint that's
responsible for setting up the initial scale, but that's not how things are at
present.)

[tommycli, 2015/03/06 21:30:55]

Done. Okay cool. That's the same thing as bauerb said, so I'm going to go with
that.

+
   web_view_->layout();
   web_view_->paint(canvas, paint_rect);
 
+  // Reapply the container's device scale factor for resource loading.

[tommycli, 2015/03/06 00:19:23]

Not sure if this is actually needed. It doesn't seem to have an effect in my
testing, but it seems like it would be good.

[jbroman, 2015/03/06 20:25:49]

See above.

[tommycli, 2015/03/06 21:30:55]

Done.

+  if (container_)
+    web_view_->setDeviceScaleFactor(container_->deviceScaleFactor());
+
   canvas->restore();
 }