Applied google3-readability-pass-trivial-by-value ClangTidy fixes to all of google3.

http://g3doc/devtools/cymbal/clang_tidy/g3doc/checks/google3-readability-pass-trivial-by-value

This check finds function signatures that pass trivial types by `const Type&`.
It is simpler and more efficient to pass these types by value.

The changelist was automatically generated using the apply_fixes.sh script:
  ./devtools/cymbal/clang_tidy/apply_fixes.sh --checks=-*,google3-readability-pass-trivial-by-value

WARNING: Automatically generated changes should be carefully inspected. For most
ClangTidy warnings multiple alternative fixes are possible and only one of them
is suggested. There's no guarantee that it will be the best one (or even a right
fix). The amount of reviewers' attention to automated changes should be at least
the same as for manually written code.

Tested:
    TAP --sample ran all affected tests and none failed
    http://test/OCL:347842546:BASE:347811712:1608141504976:7eb78f31
PiperOrigin-RevId: 348605790

Author: Googler

database/tests/desktop/core/tree_test.cc

@@ -607,7 +607,7 @@ VisitedList GetVisitedChildStdFunction(const Tree<int>& tree,
                                        const Path& input_path) {
   VisitedList visited;
 
-  tree.CallOnEach(input_path, [&](const Path& path, const int& value) {
+  tree.CallOnEach(input_path, [&](const Path& path, const int value) {
     visited.push_back(std::make_pair(path.str(), value));
   });
   return visited;