Web MIDI: use GetVendorName() result only if it is available

media/midi/midi_manager_win.cc

Index: media/midi/midi_manager_win.cc
diff --git a/media/midi/midi_manager_win.cc b/media/midi/midi_manager_win.cc
index 926fe291483348d45310b2b285b90c9c2b8198ab..44110f2c6e3d0ce4c10c68821a222309bd05ecbd 100644
--- a/media/midi/midi_manager_win.cc
+++ b/media/midi/midi_manager_win.cc
@@ -291,8 +291,11 @@ struct MidiDeviceInfo final {
 };
 
 std::string GetManufacturerName(const MidiDeviceInfo& info) {
-  if (info.is_usb_device)
-    return device::UsbIds::GetVendorName(info.usb_vendor_id);
+  if (info.is_usb_device) {
+    const char* name = device::UsbIds::GetVendorName(info.usb_vendor_id);
+    if (name)

[yukawa, 2015/04/06 17:24:55]

Probably
  return std::string(name ? name : "");
might be better because |info.manufacturer_id| is almost always the same value
when |info.is_usb_device| is true, and the actual value of 
|info.manufacturer_id| is probably useless for us to distinguish device
manufacture.

Another idea is to use StringPiece, which is NULL-tolerant.

base::StringPiece GetManufacturerName(const MidiDeviceInfo& info) {
  if (info.is_usb_device) {
    // Note: |base::StringPiece| can be constructed even from nullptr.
    return device::UsbIds::GetVendorName(info.usb_vendor_id);
  }
  ....
}

+      return name;
+  }
 
   switch (info.manufacturer_id) {
     case MM_MICROSOFT: