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/cancelable_callback_unittest.cc b/base/cancelable_callback_unittest.cc
index e793a83..373498c 100644
--- a/base/cancelable_callback_unittest.cc
+++ b/base/cancelable_callback_unittest.cc
@@ -23,7 +23,8 @@
 class TestRefCounted : public RefCountedThreadSafe<TestRefCounted> {
  private:
   friend class RefCountedThreadSafe<TestRefCounted>;
-  ~TestRefCounted() {};
+  ~TestRefCounted() = default;
+  ;
 };
 
 void Increment(int* count) { (*count)++; }