Reland: Add --no-history option to fetch and gclient for shallow clones.

gclient_scm.py

Index: gclient_scm.py
diff --git a/gclient_scm.py b/gclient_scm.py
index a87032e749902122c676b6621dde4fec33f8f232..d457a5c5a5fc8b7f6450656d0a5ce45fcc1192ed 100644
--- a/gclient_scm.py
+++ b/gclient_scm.py
@@ -825,6 +825,25 @@ class GitWrapper(SCMWrapper):
     # create it, so we need to do it manually.
     parent_dir = os.path.dirname(self.checkout_path)
     gclient_utils.safe_makedirs(parent_dir)
+
+    template_dir = None
+    if hasattr(options, 'no_history') and options.no_history:
+      if gclient_utils.IsGitSha(revision):
+        # In the case of a subproject, the pinned sha is not necessarily the
+        # head of the remote branch (so we can't just use --depth=N). Instead,
+        # we tell git to fetch all the remote objects from SHA..HEAD by means of
+        # a template git dir which has a 'shallow' file pointing to the sha.
+        template_dir = tempfile.mkdtemp(
+            prefix='_gclient_gittmp_%s' % os.path.basename(self.checkout_path),
+            dir=parent_dir)
+        self._Run(['init', '--bare', template_dir], options, cwd=self._root_dir)
+        with open(os.path.join(template_dir, 'shallow'), 'w') as template_file:
+          template_file.write(revision)
+        clone_cmd.append('--template=' + template_dir)
+      else:
+        # Otherwise, we're just interested in the HEAD. Just use --depth.
+        clone_cmd.append('--depth=1')
+
     tmp_dir = tempfile.mkdtemp(
         prefix='_gclient_%s_' % os.path.basename(self.checkout_path),
         dir=parent_dir)
@@ -841,6 +860,8 @@ class GitWrapper(SCMWrapper):
       if os.listdir(tmp_dir):
         self.Print('_____ removing non-empty tmp dir %s' % tmp_dir)
       gclient_utils.rmtree(tmp_dir)
+      if template_dir:
+        gclient_utils.rmtree(template_dir)
     self._UpdateBranchHeads(options, fetch=True)
     self._Checkout(options, revision.replace('refs/heads/', ''), quiet=True)
     if self._GetCurrentBranch() is None: