Allow setContentDecryptionModule() to get called when setting is done.

media/base/test_helpers.cc

Index: media/base/test_helpers.cc
diff --git a/media/base/test_helpers.cc b/media/base/test_helpers.cc
index 929b2f3c725c70ee4fa26fc770ee0e9e827112d6..94ee4ac0a24bdafabef8022ac0541a18b58e1d7b 100644
--- a/media/base/test_helpers.cc
+++ b/media/base/test_helpers.cc
@@ -242,4 +242,21 @@ bool VerifyFakeVideoBufferForTest(
           height == config.coded_size().height());
 }
 
+MatchingCallbackVerifier::MatchingCallbackVerifier() : a_called_(false) {
+}
+
+MatchingCallbackVerifier::~MatchingCallbackVerifier() {
+  EXPECT_FALSE(a_called_);
+}
+
+void MatchingCallbackVerifier::A() {
+  EXPECT_FALSE(a_called_);
+  a_called_ = true;
+}
+
+void MatchingCallbackVerifier::B() {
+  EXPECT_TRUE(a_called_);
+  a_called_ = false;
+}
+
 }  // namespace media