Remove timeout behavior from Windows serial I/O

Reads on the Windows impl of SerialConnection were erroneously set to
wait for up to 10ms before completing with less than the requested
amount of data.

They will now complete immediately with any available data, without
waiting.

BUG=324886

Review URL: https://codereview.chromium.org/100813002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238367 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/extensions/api/serial/serial_connection_win.cc

@@ -158,12 +158,12 @@ bool SerialConnection::ConfigurePort(
 }
 
 bool SerialConnection::PostOpen() {
-  // Set a very brief read interval timeout. This prevents the asynchronous I/O
-  // system from being way too eager to fire off completion events which would
-  // in turn result in a lot of onReceive events being fired (i.e., one for
-  // every individual byte received on the serial buffer.)
+  // A ReadIntervalTimeout of MAXDWORD will cause async reads to complete
+  // immediately with any data that's available, even if there is none.
+  // This is OK because we never issue a read request until WaitCommEvent
+  // signals that data is available.
   COMMTIMEOUTS timeouts = { 0 };
-  timeouts.ReadIntervalTimeout = 10;
+  timeouts.ReadIntervalTimeout = MAXDWORD;
   if (!::SetCommTimeouts(file_, &timeouts)) {
     return false;
   }