When running gclient sync after the merge point, the previous .git directory (containing all the local branches) for blink will be saved in //src/../old_src_third_party_WebKit.git

For each local branch, run the following steps:

• Create a patch file
• git diff origin/master...branch_name > /tmp/old-blink.patch

• Recreate the branch
  
  git new-branch old-blink
• Apply the patch
• git apply -3 --directory third_party/WebKit/ /tmp/old-blink.patch

If you have the patch locally as a git branch, migrating that would be easier. Otherwise, follow these steps:

1. Download the raw patch from codereview.chomium.org/123456
2. Create a new local git branch in a post-merge checkout
   
   git new-branch issue123456
3. Apply the patch
   
   git apply -3 --directory third_party/WebKit/ issue123456_1001.diff
4. Add new files and commit changes
5. Upload to a new CL

If you use git log or similar over the merge commit, use --first-parent to walk up only in the chromium history.

The active releases branches will be merged (i.e. won't have a third_party/WebKit subproject) as well.

For CL that get landed after the merge day, it won't be any different than cherry-picking a chromium CL. Just follow the git-drover man page.

To cherry-pick a blink CL that was landed before the merge day:

• Find the corresponding commit that you want to cherry-pick in the chromium master and note its SHA1 (note: it will have a different SHA1 than what reported in the codereview.chromium.org/NNNN) 
  e.g., if you want to cherry-pick https://codereview.chromium.org/1340403003
  
• git log origin/master --grep codereview.chromium.org/1340403003 -- third_party/WebKit

commit c614d6deae3c6e4cc0bfbb60bb15a17305b418b7
Author: ....
• Follow the git-drover documentation using SHA1 above when doing git cherry-pick -x 

Use fetch chromium instead.

Converting revision range links from SVN to git

Bisecting across the merge point

• Bisect scripts (src/tools/bisect-builds.py) and bots should Just Work TM. File a bug if that is not the case.
• Doing a git bisect on a revision range that includes the merge point requires a little trick. (See [chromium-dev] Merge of Chromium and Blink repositories - git bisect is broken? for context and details)
• The trick consists in convincing git that the merge commit (b59b6df51) did NOT pull in the blink history (70aa692d6) using grafts
• git replace --graft b59b6df51 70aa692d6

# Do the git bisect as usual
git bisect start GOOD_SHA1 BAD_SHA1 

# Remove the grafts at the end
$ git replace -d b59b6df51