Fix issue 420: accept truncated log files.

tools/logreader.js

 // Copyright 2009 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 276 matching lines @@
         continue;
       }
       if (line.charAt(0) == '#' ||
           line.substr(0, line.indexOf(',')) in this.backRefsCommands_) {
         line = this.expandBackRef_(line);
       }
       var fields = csvParser.parseLine(line);
       this.dispatchLogRow_(fields);
     }
   } catch (e) {
-    this.printError('line ' + (i + 1) + ': ' + (e.message || e));
-    throw e;
+    // An error on the last line is acceptable since log file can be truncated.
+    if (i < n - 1) {
+      this.printError('line ' + (i + 1) + ': ' + (e.message || e));
+      throw e;
+    }
   }
 };
 
 
 /**
  * Processes repeat log record. Expands it according to calls count and
  * invokes processing.
  *
  * @param {number} count Count.
  * @param {Array.<string>} cmd Parsed command.
  * @private
  */
 devtools.profiler.LogReader.prototype.processRepeat_ = function(count, cmd) {
   // Replace the repeat-prefixed command from backrefs list with a non-prefixed.
   this.backRefs_[0] = cmd.join(',');
   for (var i = 0; i < count; ++i) {
     this.dispatchLogRow_(cmd);
   }
 };