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

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: Ib4d1680c615407583a6ad72ce51634d2f444db99
Reviewed-on: https://chromium-review.googlesource.com/789742
Reviewed-by: Jeremy Roman <[email protected]>
Commit-Queue: Chris Watkins <[email protected]>
Cr-Commit-Position: refs/heads/master@{#520826}
diff --git a/gin/v8_foreground_task_runner_base.cc b/gin/v8_foreground_task_runner_base.cc
index 53f6104..7c21af8 100644
--- a/gin/v8_foreground_task_runner_base.cc
+++ b/gin/v8_foreground_task_runner_base.cc
@@ -6,9 +6,9 @@
 
 namespace gin {
 
-V8ForegroundTaskRunnerBase::V8ForegroundTaskRunnerBase() {}
+V8ForegroundTaskRunnerBase::V8ForegroundTaskRunnerBase() = default;
 
-V8ForegroundTaskRunnerBase::~V8ForegroundTaskRunnerBase() {}
+V8ForegroundTaskRunnerBase::~V8ForegroundTaskRunnerBase() = default;
 
 void V8ForegroundTaskRunnerBase::EnableIdleTasks(
     std::unique_ptr<V8IdleTaskRunner> idle_task_runner) {