[Extensions] Code Cleanup - Remove redundant smart-ptr get()s

Given std::unique_ptr<T> t, t.get()-> is the same as t->.
Similarly, *t.get() is the same as *t. Simplify extensions
code to conform.

Generated with clang-tidy.
See https://chromium.googlesource.com/chromium/src/+/master/docs/clang_tidy.md

BUG=None

Review-Url: https://codereview.chromium.org/2152373003
Cr-Commit-Position: refs/heads/master@{#406117}
diff --git a/chrome/browser/extensions/extension_management_test_util.cc b/chrome/browser/extensions/extension_management_test_util.cc
index e974db4..68383fb 100644
--- a/chrome/browser/extensions/extension_management_test_util.cc
+++ b/chrome/browser/extensions/extension_management_test_util.cc
@@ -60,7 +60,7 @@
 
 void ExtensionManagementPrefUpdaterBase::
     ClearInstallationModesForIndividualExtensions() {
-  for (base::DictionaryValue::Iterator it(*pref_.get()); !it.IsAtEnd();
+  for (base::DictionaryValue::Iterator it(*pref_); !it.IsAtEnd();
        it.Advance()) {
     DCHECK(it.value().IsType(base::Value::TYPE_DICTIONARY));
     if (it.key() != schema::kWildcard) {