mediastream: fix an implicit conversion warning

The warning is upset that we're comparing a double,
`ConstraintMax(constraint)`, against an enum,
`media::limits::kMaxFramesPerSecond`. Casting makes it happy.

Bug: 1058218
Change-Id: Ib96907e200228ffc28260d4e3de03e767c9352af
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2096028Reviewed-by: Henrik Boström <hbos@chromium.org>
Commit-Queue: George Burgess <gbiv@chromium.org>
Cr-Commit-Position: refs/heads/master@{#749288}

third_party/blink/renderer/modules/mediastream/media_stream_constraints_util_video_device.cc

@@ -352,9 +352,10 @@ class CandidateFormat {
   bool SatisfiesFrameRateConstraint(const DoubleConstraint& constraint) {
     double constraint_min =
         ConstraintHasMin(constraint) ? ConstraintMin(constraint) : -1.0;
-    double constraint_max = ConstraintHasMax(constraint)
-                                ? ConstraintMax(constraint)
-                                : media::limits::kMaxFramesPerSecond;
+    double constraint_max =
+        ConstraintHasMax(constraint)
+            ? ConstraintMax(constraint)
+            : static_cast<double>(media::limits::kMaxFramesPerSecond);
     bool constraint_min_out_of_range =
         ((constraint_min > NativeFrameRate()) ||
          (constraint_min > MaxFrameRateConstraint().value_or(