Fix SnapshotBrowserAgent (and similar) header style to match the updated
style guides.

– Updated headers to match the recommendations from the style guide

Bug: 1322894
Change-Id: I244ce55c815b514ddc3f037da752180a53bdcaa9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3629585
Commit-Queue: Petro Akzhygitov <pakzhygitov@google.com>
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Cr-Commit-Position: refs/heads/main@{#999927}
diff --git a/ios/chrome/browser/snapshots/snapshot_browser_agent.h b/ios/chrome/browser/snapshots/snapshot_browser_agent.h
index 0159cc27..2e52dda 100644
--- a/ios/chrome/browser/snapshots/snapshot_browser_agent.h
+++ b/ios/chrome/browser/snapshots/snapshot_browser_agent.h
@@ -14,16 +14,15 @@
 @class SnapshotCache;
 
 // Associates a SnapshotCache to a Browser.
-class SnapshotBrowserAgent : BrowserObserver,
+class SnapshotBrowserAgent : public BrowserObserver,
                              public WebStateListObserver,
                              public BrowserUserData<SnapshotBrowserAgent> {
  public:
-  SnapshotBrowserAgent();
-  ~SnapshotBrowserAgent() override;
-
   SnapshotBrowserAgent(const SnapshotBrowserAgent&) = delete;
   SnapshotBrowserAgent& operator=(const SnapshotBrowserAgent&) = delete;
 
+  ~SnapshotBrowserAgent() override;
+
   // Set a session identification string that will be used to locate the
   // snapshots directory. Setting this more than once on the same agent is
   // probably a programming error.