Fix buffer overflow in ContentPasswordManagerDriverFactory

There is a heap buffer overflow in ContentPasswordManagerDriverFactory::DidFinishNavigation.
This bug is a consequence of race between RenderFrameDeleted and DidFinishNavigation methods
of ContentPasswordManagerDriverFactory class and occures during execution in following test:
browser_tests.MimeHandlerViewCrossProcessTest.NavigationRaceFromEmbedder/1

Change-Id: Ifefb065c4ce2f0603c143ce777982e3fad60bcc2
Reviewed-on: https://chromium-review.googlesource.com/c/1493052
Commit-Queue: Vadym Doroshenko <dvadym@chromium.org>
Reviewed-by: Vadym Doroshenko <dvadym@chromium.org>
Cr-Commit-Position: refs/heads/master@{#636396}

components/password_manager/content/browser/content_password_manager_driver_factory.cc

@@ -104,8 +104,8 @@ void ContentPasswordManagerDriverFactory::DidFinishNavigation(
   if (!navigation_handle->HasCommitted())
     return;
 
-  frame_driver_map_.find(navigation_handle->GetRenderFrameHost())
-      ->second->DidNavigateFrame(navigation_handle);
+  if (auto* driver = GetDriverForFrame(navigation_handle->GetRenderFrameHost()))
+    driver->DidNavigateFrame(navigation_handle);
 }
 
 void ContentPasswordManagerDriverFactory::RequestSendLoggingAvailability() {