This turns the AtomViewMsg_Offscreen message, which only called the global setter blink::WebView::SetUseExternalPopupMenus(false) to get Chrome to render popup menus in the renderer instead of externally on macOS, into a command-line renderer flag --offscreen which does the same thing, except at render thread startup time, which is where Chromium sets the flag: https://chromium.googlesource.com/chromium/src/+/refs/tags/75.0.3755.3/content/renderer/render_thread_impl.cc#728.
This was the last usage of RenderViewObserver in our codebase, so this PR also removes that class.
* fix: make OSR work with viz compositor
* fix: update OSR patch
* fix: update patch again
* fix: update viz_osr.patch for macOS
* fix: gn check warnings
* chore: no need to change SoftwareOutputDeviceWinProxy
* chore: add check in case we missed something
* fix: consider scale factor when compare size
* fix: make GPU OSR work
* fix: autofill popups with OSR
* chore: use UNIX line ending for osr_video_consumer
* chore: code is already in defined(OS_MACOSX)
* fix: share same OSR implementation on macOS
This should also fix the crash when there is navigation on macOS.
* test: osr window should not crash after navigation
* fix: make osr work on Mac properly
* fix: software osr on windows
* fix: software osr on Linux
* fix: compilation error introduced with rebase
* fix: split local surface id allocation into two
* Update osr_host_display_client_mac.mm
* chore: update copyright year
* fix: update patch
* fix: update and enable osr
* fix: update MacHelper view to call GetNativeView
* style: move stuff around to make more sense
* chore: move OSR related things in SetOwnerWindow to CommonWebContentsDelegate
* fix: avoid crashing when GetOffscreenRenderWidgetHostView is called
* fix: specify default for current_device_scale_factor_
