Enable cpplint and fix cpplint errors in webrtc/api

webrtc/api/statstypes.h

Index: webrtc/api/statstypes.h
diff --git a/webrtc/api/statstypes.h b/webrtc/api/statstypes.h
index 8f90c886861e2016b452bc8e8d7b319a158278e5..40d26ab284c0ee9d64d0a7cd43a55b06401936f3 100644
--- a/webrtc/api/statstypes.h
+++ b/webrtc/api/statstypes.h
@@ -18,6 +18,7 @@
 #include <list>
 #include <map>
 #include <string>
+#include <vector>
 
 #include "webrtc/base/basictypes.h"
 #include "webrtc/base/constructormagic.h"
@@ -234,7 +235,7 @@ class StatsReport {
     // Protected since users of the IdBase type will be using the Id typedef.
     virtual bool Equals(const IdBase& other) const;
 
-    IdBase(StatsType type);  // Only meant for derived classes.
+    explicit IdBase(StatsType type);  // Only meant for derived classes.
     const StatsType type_;
 
     static const char kSeparator = '_';