components: default the user-defined empty ctor and dtor where possible

I need an owner's approval please for changes under:
components/ui_devtools

This is a mechanical change. There are a few instances (but not all)
of empty user-defined constructors and destructors which can be
defaulted in the /components code.

This CL was uploaded by git cl split.

[email protected]

Bug: 371316188
Change-Id: I0bfcacec6faf5e24a6d1cbefc4ae587577bddea8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5917421
Auto-Submit: Sorin Jianu <[email protected]>
Reviewed-by: Leonard Grey <[email protected]>
Commit-Queue: Leonard Grey <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1366139}
diff --git a/components/ui_devtools/page_agent.cc b/components/ui_devtools/page_agent.cc
index eacfd1e..e16c899 100644
--- a/components/ui_devtools/page_agent.cc
+++ b/components/ui_devtools/page_agent.cc
@@ -8,6 +8,6 @@
 
 PageAgent::PageAgent(DOMAgent* dom_agent) : dom_agent_(dom_agent) {}
 
-PageAgent::~PageAgent() {}
+PageAgent::~PageAgent() = default;
 
 }  // namespace ui_devtools