Revert "Reland "gclient: Require a target ref when applying patches.""

This reverts commit 822dbc51a298688c61e4dd8c40fbc714e1460663.

Reason for revert:
Skia autoroller is complaining
https://skia-review.googlesource.com/c/buildbot/+/219338

Original change's description:
> Reland "gclient: Require a target ref when applying patches."
> 
> This is a reland of 1d6478a5ffed7d272a7910d678e0a35d2f9fd69b
> 
> Original change's description:
> > gclient: Require a target ref when applying patches.
> > 
> > Bug: 956807
> > Change-Id: Icfffe965f9f4651f22e8ba32c60133a5620bb350
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1616804
> > Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>
> > Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>
> 
> Bug: 956807
> Change-Id: I3de8475a091ce6a2a14ff7dcfb92507a205ef78c
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1623594
> Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>
> Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>

TBR=borenet@chromium.org,tandrii@chromium.org,ehmaldonado@chromium.org

Change-Id: I14a70206a34f7024abc21039806f23dc7cf56bb6
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 956807
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1648321
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>
diff --git a/gclient.py b/gclient.py
index fd67a29..71ec2b1 100755
--- a/gclient.py
+++ b/gclient.py
@@ -1574,12 +1574,13 @@
       return patch_refs, target_branches
     for given_patch_ref in self._options.patch_refs:
       patch_repo, _, patch_ref = given_patch_ref.partition('@')
-      if not patch_repo or not patch_ref or ':' not in patch_ref:
+      if not patch_repo or not patch_ref:
         raise gclient_utils.Error(
             'Wrong revision format: %s should be of the form '
-            'patch_repo@target_branch:patch_ref.' % given_patch_ref)
-      target_branch, _, patch_ref = patch_ref.partition(':')
-      target_branches[patch_repo] = target_branch
+            'patch_repo@[target_branch:]patch_ref.' % given_patch_ref)
+      if ':' in patch_ref:
+        target_branch, _, patch_ref = patch_ref.partition(':')
+        target_branches[patch_repo] = target_branch
       patch_refs[patch_repo] = patch_ref
     return patch_refs, target_branches
 
@@ -2597,7 +2598,7 @@
   parser.add_option('--patch-ref', action='append',
                     dest='patch_refs', metavar='GERRIT_REF', default=[],
                     help='Patches the given reference with the format '
-                         'dep@target-ref:patch-ref. '
+                         'dep@[target-ref:]patch-ref. '
                          'For |dep|, you can specify URLs as well as paths, '
                          'with URLs taking preference. '
                          '|patch-ref| will be applied to |dep|, rebased on top '
@@ -2607,7 +2608,10 @@
                          '|target-ref| is the target branch against which a '
                          'patch was created, it is used to determine which '
                          'commits from the |patch-ref| actually constitute a '
-                         'patch.')
+                         'patch. If not given, we will iterate over all remote '
+                         'branches and select one that contains the revision '
+                         '|dep| is synced at. '
+                         'WARNING: |target-ref| will be mandatory soon.')
   parser.add_option('--with_branch_heads', action='store_true',
                     help='Clone git "branch_heads" refspecs in addition to '
                          'the default refspecs. This adds about 1/2GB to a '