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..b37dc0e8f8ab46b8a9c346b9c83c381310c47ed9 100644
--- a/media/base/test_helpers.cc
+++ b/media/base/test_helpers.cc
@@ -242,4 +242,21 @@ bool VerifyFakeVideoBufferForTest(
           height == config.coded_size().height());
 }
 
+CallbackPairChecker::CallbackPairChecker() : expecting_b_(false) {
+}
+
+CallbackPairChecker::~CallbackPairChecker() {
+  EXPECT_FALSE(expecting_b_);
+}
+
+void CallbackPairChecker::RecordACalled() {
+  EXPECT_FALSE(expecting_b_);
+  expecting_b_ = true;
+}
+
+void CallbackPairChecker::RecordBCalled() {
+  EXPECT_TRUE(expecting_b_);
+  expecting_b_ = false;
+}
+
 }  // namespace media