Web MIDI: enable dynamic instantiation mode by default

To prepare for dynamic instantiation launch on macOS, flip the
default behavior to use the dynamic instantiation mode by default
even on macOS and Android.

The feature will be launched at m62 on macOS, and at 63 on Android.

Bug: 672793
Change-Id: Ic4f8dc985c07cd388842ad72381bae1be078ae62
Reviewed-on: https://chromium-review.googlesource.com/712494
Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Commit-Queue: Takashi Toyoshima <toyoshim@chromium.org>
Cr-Commit-Position: refs/heads/master@{#508614}
diff --git a/media/midi/midi_switches.cc b/media/midi/midi_switches.cc
index ced7809..84e96c53 100644
--- a/media/midi/midi_switches.cc
+++ b/media/midi/midi_switches.cc
@@ -19,7 +19,7 @@
 #endif
 
 const base::Feature kMidiManagerDynamicInstantiation{
-    "MidiManagerDynamicInstantiation", base::FEATURE_DISABLED_BY_DEFAULT};
+    "MidiManagerDynamicInstantiation", base::FEATURE_ENABLED_BY_DEFAULT};
 
 }  // namespace features
 }  // namespace midi