Use base namespace for string16 in components and cloud_print.

components/sessions/serialized_navigation_entry.cc

Index: components/sessions/serialized_navigation_entry.cc
diff --git a/components/sessions/serialized_navigation_entry.cc b/components/sessions/serialized_navigation_entry.cc
index be00bd72cae6320568e1b6895ee6159ae6fdc881..5506220d3eba6c442a23a5505ae60a211cbce9d3 100644
--- a/components/sessions/serialized_navigation_entry.cc
+++ b/components/sessions/serialized_navigation_entry.cc
@@ -176,19 +176,19 @@ void WriteStringToPickle(Pickle* pickle,
   }
 }
 
-// string16 version of WriteStringToPickle.
+// base::string16 version of WriteStringToPickle.
 //
 // TODO(akalin): Unify this, too.
 void WriteString16ToPickle(Pickle* pickle,
                            int* bytes_written,
                            int max_bytes,
-                           const string16& str) {
+                           const base::string16& str) {
   int num_bytes = str.size() * sizeof(char16);
   if (*bytes_written + num_bytes < max_bytes) {
     *bytes_written += num_bytes;
     pickle->WriteString16(str);
   } else {
-    pickle->WriteString16(string16());
+    pickle->WriteString16(base::string16());
   }
 }