Use new Base64 encode functions.

[ Merge of http://go/wvgerrit/119806 ]

This change replaces all calls for base64 encoding which first converts
a string to a vector.  The new base64 encoding function allow for
encoding binary data contained within strings.

Bug: 181732604
Test: Android unittests
Change-Id: Ibfe79dba99e6a2ee2f2a96e85b62fbd22519aea7

libwvdrmengine/cdm/test/request_license_test.cpp

@@ -8,6 +8,7 @@
 #include <chrono>
 #include <sstream>
 #include <thread>
+#include <utility>
 
 #include <android-base/properties.h>
 #include <gmock/gmock.h>
@@ -2564,9 +2565,9 @@ TEST_F(WvCdmRequestLicenseTest, ProvisioningRevocationTest) {
     signed_response.SerializeToString(&response);
 
     if (!wvcdm::Properties::provisioning_messages_are_binary()) {
-      std::vector<uint8_t> response_vec(response.begin(), response.end());
+      const std::string binary_response = std::move(response);
       response = "\"signedResponse\": \"";
-      response.append(wvcdm::Base64SafeEncode(response_vec));
+      response.append(wvcdm::Base64SafeEncode(binary_response));
       response.append("\"");
     }