code: function tryFile(fileName, failedLookupLocation, onlyRecordFailures, state) {
          if (!onlyRecordFailures && state.host.fileExists(fileName)) {
              if (state.traceEnabled) {
                  ts.trace(state.host, ts.Diagnostics.File_0_exist_use_it_as_a_name_resolution_result, fileName);
              }
              return fileName;
          }
          else {
              if (state.traceEnabled) {
                  ts.trace(state.host, ts.Diagnostics.File_0_does_not_exist, fileName);
              }
              failedLookupLocation.push(fileName);
              return undefined;
          }
      }
docs: Return the file if it exists.