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/test/test_base.cpp

@@ -291,7 +291,6 @@ WvCdmTestBase::WvCdmTestBase()
 
 void WvCdmTestBase::Provision() {
   CdmProvisioningRequest prov_request;
-  CdmProvisioningRequest binary_prov_request;
   std::string provisioning_server_url;
   CdmCertificateType cert_type = kCertificateWidevine;
   std::string cert_authority;
@@ -331,9 +330,7 @@ void WvCdmTestBase::Provision() {
     ASSERT_EQ(NO_ERROR, result);
 
     if (binary_provisioning_) {
-      binary_prov_request = prov_request;
-      prov_request = std::string(Base64SafeEncodeNoPad(std::vector<uint8_t>(
-          binary_prov_request.begin(), binary_prov_request.end())));
+      prov_request = Base64SafeEncodeNoPad(prov_request);
     }
 
     LOGV("Provisioning request: req = %s", prov_request.c_str());