Should not expose proto headers in public SDK headers and not include absl

mutex.h in public SDK headers.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=249330673

sdk/external/common/wvpl/wvpl_sdk_environment.h

@@ -13,7 +13,6 @@
 #include <string>
 
 #include "sdk/external/common/wvpl/wvpl_types.h"
-#include "protos/public/drm_certificate.pb.h"
 
 namespace widevine {
 class DeviceCertificateStatusList;
@@ -111,8 +110,7 @@ class WvPLSDKEnvironment {
 
  private:
   // Get the expected service type for drm service certificate.
-  virtual widevine::DrmCertificate::ServiceType
-  GetExpectedServiceCertificateType();
+  virtual int GetExpectedServiceCertificateType();
 
   // Check the type of |service_certificate|. Returns "OK" if the cert can be
   // used for the current SDK, else an error status.