Use static_cast instead of reinterpret_cast for downcasting

static_cast is better suited for downcasting since it can check that the
types are related.

/components/plugins
This CL was uploaded by git cl split.

R=tommycli@chromium.org

Change-Id: Ic82fae77b2f270d0b10e9354d903498d7c33117a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2435331
Auto-Submit: Kevin McNee <mcnee@chromium.org>
Reviewed-by: Tommy Li <tommycli@chromium.org>
Commit-Queue: Kevin McNee <mcnee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#811722}

components/plugins/renderer/webview_plugin.cc

@@ -223,7 +223,7 @@ blink::WebInputEventResult WebViewPlugin::HandleInputEvent(
   if (event.GetType() == blink::WebInputEvent::Type::kContextMenu) {
     if (delegate_) {
       const WebMouseEvent& mouse_event =
-          reinterpret_cast<const WebMouseEvent&>(event);
+          static_cast<const WebMouseEvent&>(event);
       delegate_->ShowContextMenu(mouse_event);
     }
     return blink::WebInputEventResult::kHandledSuppressed;