Add DCHECKs to match cherrypick

Bug: 144861135
Test: None
Change-Id: I0536d253e12cd3a2295ef667d3c8016f498b4ad3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1936891Reviewed-by: Daniel Nicoara <dnicoara@chromium.org>
Commit-Queue: Daniel Nicoara <dnicoara@chromium.org>
Cr-Commit-Position: refs/heads/master@{#719184}

chromecast/browser/webview/web_content_controller.cc

@@ -161,6 +161,8 @@ void WebContentController::AttachTo(aura::Window* window, int window_id) {
 
 void WebContentController::ProcessInputEvent(const webview::InputEvent& ev) {
   content::WebContents* contents = GetWebContents();
+  DCHECK(contents);
+  DCHECK(contents->GetNativeView());
   if (!contents->GetNativeView()->CanFocus())
     return;
   // Ensure this web contents has focus before sending it input.