Add .clean_trace() to the APIs to delete the stale traces.

tools/isolate/trace_inputs.py

Index: tools/isolate/trace_inputs.py
diff --git a/tools/isolate/trace_inputs.py b/tools/isolate/trace_inputs.py
index 78918a6800c3e133f9c8cedb1df29131f2c47901..f49b8155b2250003fa389292bc0f822bc2cfe689 100755
--- a/tools/isolate/trace_inputs.py
+++ b/tools/isolate/trace_inputs.py
@@ -389,6 +389,12 @@ class Strace(object):
         else:
           self.non_existent.add(filepath)
 
+  @staticmethod
+  def clean_trace(logname):
+    """Deletes the old log."""
+    if os.path.isfile(logname):
+      os.remove(logname)

[MAD, 2012/05/11 18:51:38]

Shouldn't we try to catch these?

"On Windows, attempting to remove a file that is in use causes an exception to
be raised"

And if so, instead of repeating this code in all classes, why not have a method
to retrieve all log file names in an array and iterate over it with a single
exception proof remove file implementation... No?

[M-A Ruel, 2012/05/11 18:57:25]

I prefer the script to crash if the files can't be removed. Since it'll fail
later anyway.

BTW, you meant line 1029. line 396 is never executed on windows.
Exceptions are only an issue on Windows. And I want them to be fatal anyway. I
also prefer the caller to not have to do anything with the function result.

+
   @classmethod
   def gen_trace(cls, cmd, cwd, logname, output):
     """Runs strace on an executable."""
@@ -699,6 +705,12 @@ class Dtrace(object):
     def _handle_ignored(_ppid, pid, function, args, result):
       logging.debug('%d %s(%s) = %s' % (pid, function, args, result))
 
+  @staticmethod
+  def clean_trace(logname):
+    """Deletes the old log."""
+    if os.path.isfile(logname):
+      os.remove(logname)
+
   @classmethod
   def gen_trace(cls, cmd, cwd, logname, output):
     """Runs dtrace on an executable."""
@@ -1013,6 +1025,14 @@ class LogmanTrace(object):
     self.IGNORED.add('\\systemroot')
     self.IGNORED = tuple(sorted(self.IGNORED))
 
+  @staticmethod
+  def clean_trace(logname):
+    """Deletes the old log."""
+    if os.path.isfile(logname):
+      os.remove(logname)
+    if os.path.isfile(logname + '.etl'):
+      os.remove(logname + '.etl')
+
   @classmethod
   def gen_trace(cls, cmd, cwd, logname, output):
     logging.info('gen_trace(%s, %s, %s, %s)' % (cmd, cwd, logname, output))
@@ -1338,8 +1358,7 @@ def trace(logfile, cmd, cwd, api, output):
   """
   cmd = fix_python_path(cmd)
   assert os.path.isabs(cmd[0]), cmd[0]
-  if os.path.isfile(logfile):
-    os.remove(logfile)
+  api.clean_trace(logfile)
   return api.gen_trace(cmd, cwd, logfile, output)