Fix leak: properly destroy TimezoneResolver instance.

BUG=416494
TEST=manual

Review URL: https://codereview.chromium.org/903733002

Cr-Commit-Position: refs/heads/master@{#315017}

chrome/browser/browser_process_platform_part_chromeos.cc

@@ -126,6 +126,9 @@ chromeos::TimeZoneResolver* BrowserProcessPlatformPart::GetTimezoneResolver() {
 }
 
 void BrowserProcessPlatformPart::StartTearDown() {
+  // interactive_ui_tests check for memory leaks before this object is
+  // destroyed.  So we need to destroy |timezone_resolver_| here.
+  timezone_resolver_.reset();
   profile_helper_.reset();
 }