Add LogDog log stream fetcher code.

web/web.py

Index: web/web.py
diff --git a/web/web.py b/web/web.py
index c32ea24085d012df2ac9df2cf6dd8c91146a2faa..2f757f47fd772d9710ad472df733aea2262719d3 100755
--- a/web/web.py
+++ b/web/web.py
@@ -120,7 +120,12 @@ class Toolchain(object):
         pipes.quote(' '.join(args)))
 
     kwargs['stderr'] = subprocess.STDOUT
-    subprocess.check_call(args, **kwargs)
+    try:
+      subprocess.check_call(args, **kwargs)
+    except subprocess.CalledProcessError as e:
+      LOGGER.warning('Non-zero return code (%d) from command.',
+          e.returncode, exc_info=LOGGER.isEnabledFor(logging.DEBUG))
+      sys.exit(e.returncode)
 
   def node(self, *args, **kwargs):
     self._call(self._node_exe, *args, **kwargs)