refactor: apply some 'clang-tidy -fix' changes (#20172)

* refactor: fix clang-tidy vector operation warnings

Fix vector population performance-inefficient-vector-operation warnings
generated by clang-tidy

* refactor: fix clang-tidy emplace_back warnings

In cases where a temporary is created to be passed
to push_back(), replace it with emplace_back().

Warning: modernize-use-emplace

* refactor: fix clang-tidy loop iteration warnings

When practical, use range-based for loops instead of C-style for loops.

clang-tiny check: modernize-loop-convert

* refactor: fix clang-tidy string initialize warning

Remove redundant empty string initialization.

clang-tidy check: readability-redundant-string-init

shell/browser/net/resolve_proxy_helper.cc

@@ -33,7 +33,7 @@ void ResolveProxyHelper::ResolveProxy(const GURL& url,
                                       ResolveProxyCallback callback) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
   // Enqueue the pending request.
-  pending_requests_.push_back(PendingRequest(url, std::move(callback)));
+  pending_requests_.emplace_back(url, std::move(callback));
 
   // If nothing is in progress, start.
   if (!binding_.is_bound()) {