Do not merge namespaces

It is good practice to not include the whole std:: namespace into
the global namespace.  This is doubly true in headers.

TEST=aidl compiles

Change-Id: I910ca8082f61cce4f23f8564b8a12c2828b75b3c
diff --git a/tools/aidl/generate_java.h b/tools/aidl/generate_java.h
index 4bfcfeb..be32364 100644
--- a/tools/aidl/generate_java.h
+++ b/tools/aidl/generate_java.h
@@ -6,7 +6,8 @@
 
 #include <string>
 
-using namespace std;
+using std::string;
+using std::vector;
 
 int generate_java(const string& filename, const string& originalSrc,
                 interface_type* iface);