Add support for entering/exiting HTML fullscreen from OOPIFs.

content/renderer/render_frame_proxy.cc

Index: content/renderer/render_frame_proxy.cc
diff --git a/content/renderer/render_frame_proxy.cc b/content/renderer/render_frame_proxy.cc
index 0509de6290e9e98524aacb606d37967ebdf5f3c2..b364b2bd6bdad4a8217f62595c2b18f4f8d6c878 100644
--- a/content/renderer/render_frame_proxy.cc
+++ b/content/renderer/render_frame_proxy.cc
@@ -274,6 +274,7 @@ bool RenderFrameProxy::OnMessageReceived(const IPC::Message& msg) {
     IPC_MESSAGE_HANDLER(FrameMsg_DidUpdateOrigin, OnDidUpdateOrigin)
     IPC_MESSAGE_HANDLER(InputMsg_SetFocus, OnSetPageFocus)
     IPC_MESSAGE_HANDLER(FrameMsg_SetFocusedFrame, OnSetFocusedFrame)
+    IPC_MESSAGE_HANDLER(FrameMsg_WillEnterFullscreen, OnWillEnterFullscreen)
     IPC_MESSAGE_UNHANDLED(handled = false)
   IPC_END_MESSAGE_MAP()
 
@@ -368,6 +369,10 @@ void RenderFrameProxy::OnSetFocusedFrame() {
   render_view_->webview()->focusDocumentView(web_frame_);
 }
 
+void RenderFrameProxy::OnWillEnterFullscreen() {
+  render_view_->webview()->willEnterFullScreen(web_frame_);
+}
+
 void RenderFrameProxy::frameDetached(DetachType type) {
   if (type == DetachType::Remove && web_frame_->parent()) {
     web_frame_->parent()->removeChild(web_frame_);