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

media/base/test_helpers.h

Index: media/base/test_helpers.h
diff --git a/media/base/test_helpers.h b/media/base/test_helpers.h
index 8dc38958f5d2a0605b435d9f599e20bb17fd8ab5..810e0866ecd08b15ce4e0c5b795e280ac8558dee 100644
--- a/media/base/test_helpers.h
+++ b/media/base/test_helpers.h
@@ -125,6 +125,19 @@ scoped_refptr<DecoderBuffer> CreateFakeVideoBufferForTest(
 bool VerifyFakeVideoBufferForTest(const scoped_refptr<DecoderBuffer>& buffer,
                                   const VideoDecoderConfig& config);
 
+// Used to verify that the each call to A() is followed by a call to B(),
+// before the next call to A(). There may be any number of pairs (including 0).
+class CallbackPairChecker {
+ public:
+  CallbackPairChecker();
+  ~CallbackPairChecker();
+  void RecordACalled();
+  void RecordBCalled();
+
+ private:
+  bool expecting_b_;
+};
+
 }  // namespace media
 
 #endif  // MEDIA_BASE_TEST_HELPERS_H_