Misc cleanup in MediaInfo proto usage

- Replaces SerializeToString with SerializeAsString.
- Construct StringPiece instead of doing implicit conversion when
  doing Base64Encode.

Change-Id: I9a9d4a138b0d949447396387adc599c7cde0b9f4

packager/media/event/muxer_listener_test_helper.cc

@@ -119,10 +119,8 @@ bool MediaInfoEqual(const MediaInfo& expect, const MediaInfo& actual) {
   // I found out here
   // https://groups.google.com/forum/#!msg/protobuf/5sOExQkB2eQ/ZSBNZI0K54YJ
   // that the best way to check equality is to serialize and check equality.
-  std::string expect_serialized;
+  std::string expect_serialized = expect.SerializeAsString();
-  std::string actual_serialized;
+  std::string actual_serialized = actual.SerializeAsString();
-  EXPECT_TRUE(expect.SerializeToString(&expect_serialized));
-  EXPECT_TRUE(actual.SerializeToString(&actual_serialized));
   EXPECT_EQ(expect_serialized, actual_serialized);
   return expect_serialized == actual_serialized;
 }

packager/mpd/base/dash_iop_mpd_notifier.cc

@@ -21,11 +21,8 @@ const int kStartingGroupId = 1;
 bool ProtectedContentEq(
     const MediaInfo::ProtectedContent& content_protection1,
     const MediaInfo::ProtectedContent& content_protection2) {
-  std::string s1;
+  return content_protection1.SerializeAsString() ==
-  std::string s2;
+         content_protection2.SerializeAsString();
-  return content_protection1.SerializeToString(&s1) &&
-         content_protection2.SerializeToString(&s2) &&
-         s1 == s2;
 }
 
 std::set<std::string> GetUUIDs(

packager/mpd/base/mpd_utils.cc

@@ -315,7 +315,9 @@ void AddContentProtectionElementsHelperTemplated(
 
     if (entry.has_pssh()) {
       std::string base64_encoded_pssh;
-      base::Base64Encode(entry.pssh(), &base64_encoded_pssh);
+      base::Base64Encode(
+          base::StringPiece(entry.pssh().data(), entry.pssh().size()),
+          &base64_encoded_pssh);
       Element cenc_pssh;
       cenc_pssh.name = kPsshElementName;
       cenc_pssh.content = base64_encoded_pssh;