Specialize media_constraints::DiscreteSet<bool>::is_universal()

It is easy to produce explicit universal cases for discrete sets of
boolean values since there are only to possible values.
This CL adds an specialization so that the common case of a set with
{true,false} is considered universal.
This helps simplify some of the constraints processing code for audio,
which contains many boolean properties.

Bug: 731170
Change-Id: Ie7cd41a161f9de93fbc13273d44d2cccaa217522
Reviewed-on: https://chromium-review.googlesource.com/c/1299004Reviewed-by: Henrik Boström <hbos@chromium.org>
Commit-Queue: Guido Urdaneta <guidou@chromium.org>
Cr-Commit-Position: refs/heads/master@{#603056}

content/renderer/media/stream/media_stream_constraints_util_sets.h

@@ -165,6 +165,13 @@ class DiscreteSet {
   std::vector<T> elements_;
 };
 
+// Special case for DiscreteSet<bool> where it is easy to produce an explicit
+// set that contains all possible elements.
+template <>
+inline bool DiscreteSet<bool>::is_universal() const {
+  return Contains(true) && Contains(false);
+}
+
 DiscreteSet<std::string> StringSetFromConstraint(
     const blink::StringConstraint& constraint);
 DiscreteSet<bool> BoolSetFromConstraint(

content/renderer/media/stream/media_stream_constraints_util_sets_unittest.cc

@@ -1265,6 +1265,10 @@ TEST_F(MediaStreamConstraintsUtilSetsTest, DiscreteSetBool) {
   set = BoolSet({true});
   intersection = set.Intersection(BoolSet({false}));
   EXPECT_TRUE(intersection.IsEmpty());
+
+  // Explicit universal set.
+  set = BoolSet({true, false});
+  EXPECT_TRUE(set.is_universal());
 }
 
 }  // namespace media_constraints