Reland MSE: Verify MediaLog events created by existing WebM unit tests

media/base/mock_media_log.h

Index: media/base/mock_media_log.h
diff --git a/media/base/mock_media_log.h b/media/base/mock_media_log.h
index 04c011633c400895680301e79746c920f0cbae65..421c2d2048144311c6b4ba24039c49c18ebb594c 100644
--- a/media/base/mock_media_log.h
+++ b/media/base/mock_media_log.h
@@ -5,9 +5,19 @@
 #ifndef MEDIA_BASE_MOCK_MEDIA_LOG_H_
 #define MEDIA_BASE_MOCK_MEDIA_LOG_H_
 
+#include <string>
+
 #include "media/base/media_log.h"
 #include "testing/gmock/include/gmock/gmock.h"
 
+// Helper macros to reduce boilerplate when verifying media log entries.
+// |outer| is the std::string searched for substring |sub|.
+#define CONTAINS_STRING(outer, sub) (std::string::npos != (outer).find(sub))
+
+// "media_log_" is expected to be a scoped_refptr<MockMediaLog>, optionally a
+// StrictMock, in scope of the usage of this macro.
+#define EXPECT_MEDIA_LOG(x) EXPECT_CALL(*media_log_, DoAddEventLogString((x)))
+
 namespace media {
 
 class MockMediaLog : public MediaLog {