Work around clang-cl bug to fix media_unittests link failure

TBR=wolenetz

Bug: 771710
Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: Id2de82dfda1fc003ed3a8095ad000e7a21f3feb9
Reviewed-on: https://chromium-review.googlesource.com/701456
Commit-Queue: Hans Wennborg <hans@chromium.org>
Reviewed-by: Matthew Wolenetz <wolenetz@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#506554}

media/filters/source_buffer_stream.cc

@@ -13,6 +13,7 @@
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
 #include "base/trace_event/trace_event.h"
+#include "build/build_config.h"
 #include "media/base/media_switches.h"
 #include "media/base/timestamp_constants.h"
 #include "media/filters/source_buffer_platform.h"
@@ -217,6 +218,9 @@ template <typename RangeClass>
 SourceBufferStream<RangeClass>::~SourceBufferStream() {}
 
 template <>
+#if defined(__clang__) && defined(OS_WIN)
+MEDIA_EXPORT  // TODO(crbug.com/771710): Remove once clang-cl is fixed.
+#endif
 void SourceBufferStream<SourceBufferRangeByDts>::OnStartOfCodedFrameGroup(
     DecodeTimestamp coded_frame_group_start_dts,
     base::TimeDelta coded_frame_group_start_pts) {
@@ -228,6 +232,9 @@ void SourceBufferStream<SourceBufferRangeByDts>::OnStartOfCodedFrameGroup(
 }
 
 template <>
+#if defined(__clang__) && defined(OS_WIN)
+MEDIA_EXPORT  // TODO(crbug.com/771710): Remove once clang-cl is fixed.
+#endif
 void SourceBufferStream<SourceBufferRangeByPts>::OnStartOfCodedFrameGroup(
     DecodeTimestamp coded_frame_group_start_dts,
     base::TimeDelta coded_frame_group_start_pts) {