repo_trace: drop notification of trace file name.

The trace file is local to the workspace. We shouldn't tell the user
that on every command that they run.

Change-Id: I8674ab485bd5142814a043a225bf8aaca7795752
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/351234
Tested-by: LaMont Jones <lamontjones@google.com>
Reviewed-by: Xin Li <delphij@google.com>

repo_trace.py

@@ -57,9 +57,9 @@ def SetTrace():
   _TRACE = True
 
 
-def _SetTraceFile():
+def _SetTraceFile(quiet):
   global _TRACE_FILE
-  _TRACE_FILE = _GetTraceFile()
+  _TRACE_FILE = _GetTraceFile(quiet)
 
 
 class Trace(ContextDecorator):
@@ -68,13 +68,21 @@ class Trace(ContextDecorator):
     """Generate nanoseconds of time in a py3.6 safe way"""
     return int(time.time() * 1e+9)
 
-  def __init__(self, fmt, *args, first_trace=False):
+  def __init__(self, fmt, *args, first_trace=False, quiet=True):
+    """Initialize the object.
+
+    Args:
+      fmt: The format string for the trace.
+      *args: Arguments to pass to formatting.
+      first_trace: Whether this is the first trace of a `repo` invocation.
+      quiet: Whether to suppress notification of trace file location.
+    """
     if not IsTrace():
       return
     self._trace_msg = fmt % args
 
     if not _TRACE_FILE:
-      _SetTraceFile()
+      _SetTraceFile(quiet)
 
     if first_trace:
       _ClearOldTraces()
@@ -109,11 +117,12 @@ class Trace(ContextDecorator):
     return False
 
 
-def _GetTraceFile():
+def _GetTraceFile(quiet):
   """Get the trace file or create one."""
   # TODO: refactor to pass repodir to Trace.
   repo_dir = os.path.dirname(os.path.dirname(__file__))
   trace_file = os.path.join(repo_dir, _TRACE_FILE_NAME)
+  if not quiet:
     print(f'Trace outputs in {trace_file}', file=sys.stderr)
   return trace_file