Run clang-tidy modernize-use-equals-{delete,default} on //base

See the bugs and cxx post for justification and details:
https://groups.google.com/a/chromium.org/forum/#!topic/cxx/RkOHzIK6Tq8

This change was done using clang-tidy as described here:
https://chromium.googlesource.com/chromium/src/+/lkcr/docs/clang_tidy.md

In some cases the the tool leaves behind a string of commas where it
replaced a member initializer list
(https://bugs.llvm.org/show_bug.cgi?id=35051). They were cleaned up with:
  git diff --name-only | \
    xargs sed -E -i 's/(^\s*|\)\s*):[ ,]*= default/\1 = default/'

BUG=778959,778957

Change-Id: I95a3f3dae4796e4a7beb77793a6101f433a2c649
Reviewed-on: https://chromium-review.googlesource.com/789718
Reviewed-by: Daniel Cheng <[email protected]>
Commit-Queue: Chris Watkins <[email protected]>
Cr-Commit-Position: refs/heads/master@{#520033}
diff --git a/base/files/file_locking_unittest.cc b/base/files/file_locking_unittest.cc
index 067ff57..e158b7d 100644
--- a/base/files/file_locking_unittest.cc
+++ b/base/files/file_locking_unittest.cc
@@ -121,7 +121,7 @@
 
 class FileLockingTest : public testing::Test {
  public:
-  FileLockingTest() {}
+  FileLockingTest() = default;
 
  protected:
   void SetUp() override {