Run clang-tidy modernize-use-equals-{delete,default} on //net, pt 1

This covers //net/base to //net/dns in alphabetical order.

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: I72d8a83ee86d833dc2caa0c3b9103689439bf443
Reviewed-on: https://chromium-review.googlesource.com/789971
Reviewed-by: David Benjamin <[email protected]>
Commit-Queue: Chris Watkins <[email protected]>
Cr-Commit-Position: refs/heads/master@{#520827}
diff --git a/net/dns/serial_worker.cc b/net/dns/serial_worker.cc
index 595c0b9..7d9f264 100644
--- a/net/dns/serial_worker.cc
+++ b/net/dns/serial_worker.cc
@@ -13,7 +13,7 @@
 
 SerialWorker::SerialWorker() : state_(IDLE) {}
 
-SerialWorker::~SerialWorker() {}
+SerialWorker::~SerialWorker() = default;
 
 void SerialWorker::WorkNow() {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);