base: Add out-of-line copy ctors for complex classes.

This patch adds out of line copy constructors for classes that our
clang-plugin considers heavy. This is an effort to enable copy
constructor checks by default.

BUG=436357
[email protected], [email protected]

Review URL: https://codereview.chromium.org/1730873002

Cr-Commit-Position: refs/heads/master@{#377443}
diff --git a/base/test/gtest_util.cc b/base/test/gtest_util.cc
index b9ab4a3a..8ad54364 100644
--- a/base/test/gtest_util.cc
+++ b/base/test/gtest_util.cc
@@ -16,6 +16,8 @@
 TestIdentifier::TestIdentifier() {
 }
 
+TestIdentifier::TestIdentifier(const TestIdentifier& other) = default;
+
 std::string FormatFullTestName(const std::string& test_case_name,
                                const std::string& test_name) {
   return test_case_name + "." + test_name;