Add unit tests for webrtc_media_stream_adapter.cc

content/renderer/media/media_stream_constraints_util.cc

Index: content/renderer/media/media_stream_constraints_util.cc
diff --git a/content/renderer/media/media_stream_constraints_util.cc b/content/renderer/media/media_stream_constraints_util.cc
index 3150c94c547d767f3d137758dba962bc0bf73c36..8c886bd68bd45f077d0f1c84428837c097282fe5 100644
--- a/content/renderer/media/media_stream_constraints_util.cc
+++ b/content/renderer/media/media_stream_constraints_util.cc
@@ -17,6 +17,7 @@ template <typename P, typename T>
 bool ScanConstraintsForExactValue(const blink::WebMediaConstraints& constraints,
                                   P picker,
                                   T* value) {
+  DCHECK(!constraints.isNull());
   const auto& the_field = constraints.basic().*picker;
   if (the_field.hasExact()) {
     *value = the_field.exact();
@@ -36,6 +37,7 @@ template <typename P, typename T>
 bool ScanConstraintsForMaxValue(const blink::WebMediaConstraints& constraints,
                                 P picker,
                                 T* value) {
+  DCHECK(!constraints.isNull());
   const auto& the_field = constraints.basic().*picker;
   if (the_field.hasMax()) {
     *value = the_field.max();
@@ -63,6 +65,7 @@ template <typename P, typename T>
 bool ScanConstraintsForMinValue(const blink::WebMediaConstraints& constraints,
                                 P picker,
                                 T* value) {
+  DCHECK(!constraints.isNull());
   const auto& the_field = constraints.basic().*picker;
   if (the_field.hasMin()) {
     *value = the_field.min();