Add DumpWithoutCrashing in RendererDidNavigateToExistingPage

This is intended to be reverted after investigating the linked bug.

BUG=688425
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_site_isolation

Review-Url: https://codereview.chromium.org/2701523004
Cr-Commit-Position: refs/heads/master@{#450900}
void NavigationControllerImpl::SetScreenshotManager(
    std::unique_ptr<NavigationEntryScreenshotManager> manager) {
  if (manager.get())
    screenshot_manager_ = std::move(manager);
  else
    screenshot_manager_.reset(new NavigationEntryScreenshotManager(this));
}

void NavigationControllerImpl::SetScreenshotManager(
    std::unique_ptr<NavigationEntryScreenshotManager> manager) {
  if (manager.get())
    screenshot_manager_ = std::move(manager);
  else
    screenshot_manager_.reset(new NavigationEntryScreenshotManager(this));
}
