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/core/src/certificate_provisioning.cpp

@@ -318,9 +318,7 @@ CdmResponseType CertificateProvisioning::GetProvisioningRequestInternal(
 
   if (!wvcdm::Properties::provisioning_messages_are_binary()) {
     // Return request as web-safe base64 string
-    std::vector<uint8_t> request_vector(serialized_request.begin(),
-                                        serialized_request.end());
-    *request = Base64SafeEncodeNoPad(request_vector);
+    *request = Base64SafeEncodeNoPad(serialized_request);
   } else {
     *request = std::move(serialized_request);
   }

libwvdrmengine/cdm/core/src/device_files.cpp

@@ -1771,9 +1771,7 @@ std::string DeviceFiles::GetUsageInfoFileName(const std::string& app_id) {
 }
 
 std::string DeviceFiles::GetFileNameSafeHash(const std::string& input) {
-  std::string hash = Md5Hash(input);
-  return wvcdm::Base64SafeEncode(
-      std::vector<uint8_t>(hash.begin(), hash.end()));
+  return wvcdm::Base64SafeEncode(Md5Hash(input));
 }
 
 }  // namespace wvcdm