Reland "Maintain change log file directly on trunk branch in push-to-trunk."

tools/push-to-trunk/git_recipes.py

Index: tools/push-to-trunk/git_recipes.py
diff --git a/tools/push-to-trunk/git_recipes.py b/tools/push-to-trunk/git_recipes.py
index fb7424f709478885ed5142d2dbb4c467f92b8222..6b54510f6365b0d3de1ffd3386570036cc382a3f 100644
--- a/tools/push-to-trunk/git_recipes.py
+++ b/tools/push-to-trunk/git_recipes.py
@@ -63,6 +63,10 @@ class GitRecipesMixin(object):
     assert name
     self.Git(MakeArgs(["checkout -f", name]))
 
+  def GitCheckoutFile(self, name):
+    assert name
+    self.Git(MakeArgs(["checkout --", name]))
+
   @Strip
   def GitCurrentBranch(self):
     for line in self.Git("status -s -b -uno").strip().splitlines():