Use pylint 2.7 for depot_tools

This includes a few fixes for specific errors, and disables several new
warnings introduced in this version, in order to allow for an incremental migration.

Bug:1262286
Change-Id: Ie97d686748c9c952e87718a65f401c5f6f80a5c9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3400616
Reviewed-by: Gavin Mak <gavinmak@google.com>
Commit-Queue: Aravind Vasudevan <aravindvasudev@google.com>
diff --git a/gclient.py b/gclient.py
index 446be28..a7cddc7 100755
--- a/gclient.py
+++ b/gclient.py
@@ -238,7 +238,7 @@
         not gclient_eval.EvaluateCondition(self._condition, self._variables)):
       return
 
-    cmd = [arg for arg in self._action]
+    cmd = list(self._action)
 
     if cmd[0] == 'python':
       cmd[0] = 'vpython'
@@ -373,8 +373,8 @@
   def target_os(self):
     if self.local_target_os is not None:
       return tuple(set(self.local_target_os).union(self.parent.target_os))
-    else:
-      return self.parent.target_os
+
+    return self.parent.target_os
 
   @property
   def target_cpu(self):
@@ -1420,7 +1420,7 @@
     if 'all' in enforced_os:
       enforced_os = self.DEPS_OS_CHOICES.values()
     self._enforced_os = tuple(set(enforced_os))
-    self._enforced_cpu = detect_host_arch.HostArch(),
+    self._enforced_cpu = (detect_host_arch.HostArch(), )
     self._root_dir = root_dir
     self._cipd_root = None
     self.config_content = None
@@ -1830,7 +1830,7 @@
     if command == 'update':
       gn_args_dep = self.dependencies[0]
       if gn_args_dep._gn_args_from:
-        deps_map = dict([(dep.name, dep) for dep in gn_args_dep.dependencies])
+        deps_map = {dep.name: dep for dep in gn_args_dep.dependencies}
         gn_args_dep = deps_map.get(gn_args_dep._gn_args_from)
       if gn_args_dep and gn_args_dep.HasGNArgsFile():
         gn_args_dep.WriteGNArgsFile()
@@ -1874,11 +1874,12 @@
         entries = {}
         def GrabDeps(dep):
           """Recursively grab dependencies."""
-          for d in dep.dependencies:
-            d.PinToActualRevision()
-            if ShouldPrintRevision(d):
-              entries[d.name] = d.url
-            GrabDeps(d)
+          for rec_d in dep.dependencies:
+            rec_d.PinToActualRevision()
+            if ShouldPrintRevision(rec_d):
+              entries[rec_d.name] = rec_d.url
+            GrabDeps(rec_d)
+
         GrabDeps(d)
         json_output.append({
             'name': d.name,
@@ -2275,7 +2276,7 @@
       if key not in self._vars:
         continue
       # Don't "override" existing vars if it's actually the same value.
-      elif self._vars[key][1] == value:
+      if self._vars[key][1] == value:
         continue
       # Anything else is overriding a default value from the DEPS.
       self._vars[key] = (hierarchy + ' [custom_var override]', value)