To reproduce: Create a new tab and open the URL in that (foreground) tab. In Safari Preferences > Tabs, deselect "select new tabs as they are created", then open the URL in a background tab. After the page is finished loading in the background tab, switch to it. Expected results: The clock should render at 1:1 resolution in the background tab, just like in the foreground tab. Actual results: The clock is pixelated in the tab that loaded in the background (looks like 2:1). Regression: Yes, shipping WebKit renders at full resolution in both tabs.
Created attachment 13393 [details] Reduction
Created attachment 13396 [details] Fall back on the main screen's scale factor if the view is not in a window The main screen's scale factor is just a better guess than the undefined result of sending a message to nil. Since canvas does not seem to support dynamic changes to this parameter (as might be necessary when the view moves from one window to another?), you're stuck with the guessed value.
Comment on attachment 13396 [details] Fall back on the main screen's scale factor if the view is not in a window Looks like the right thing to do. r=me
Committed revision 19887.