Fix webkit build failure reported by evan@

When fetching svn URL via 'git svn info --url' command
git-svn.perl script may print its progress log to stdout instead of stderr: as a result we end up using all this junk as svn repository URL.
Fix it by filtering output.

BUG=None
TEST=None

Review URL: http://codereview.chromium.org/6603022

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@76803 0039d316-1c4b-4281-b951-d872f2087c98

build/util/lastchange.py

@@ -129,14 +129,15 @@ def FetchGitSVNURL(directory):
   Returns:
     SVN URL.
   """
-  if not IsGitSVN(directory):
-    return None
-  proc = RunGitCommand(directory, ['svn', 'info', '--url'])
-  if proc:
-    output = proc.communicate()[0].strip()
-    if proc.returncode == 0:
-      return output
-  return None
+  if IsGitSVN(directory):
+    proc = RunGitCommand(directory, ['svn', 'info', '--url'])
+    if proc:
+      output = proc.communicate()[0].strip()
+      if proc.returncode == 0:
+        match = re.search(r'^\w+://.*$', output, re.M)
+        if match:
+          return match.group(0)
+  return ''
 
 
 def LookupGitSVNRevision(directory, depth):