Cleanup usage of history namespace in components/history

components/history/core/browser/page_usage_data.cc

Index: components/history/core/browser/page_usage_data.cc
diff --git a/components/history/core/browser/page_usage_data.cc b/components/history/core/browser/page_usage_data.cc
index e240ff96bec1aba3c43c82e5db87cccbf5672173..73ba3d4c7df62fb0e8f77b5fac0d56cad8480b0e 100644
--- a/components/history/core/browser/page_usage_data.cc
+++ b/components/history/core/browser/page_usage_data.cc
@@ -6,9 +6,9 @@
 
 #include <algorithm>
 
-PageUsageData::PageUsageData(history::SegmentID id)
-    : id_(id),
-      score_(0.0) {
+namespace history {
+
+PageUsageData::PageUsageData(SegmentID id) : id_(id), score_(0.0) {
 }
 
 PageUsageData::~PageUsageData() {
@@ -19,3 +19,5 @@ bool PageUsageData::Predicate(const PageUsageData* lhs,
                               const PageUsageData* rhs) {
   return lhs->GetScore() > rhs->GetScore();
 }
+
+}  // namespace history