Blink layout tests

How to land Skia changes that change Blink layout test results.

Changes that affect a small number of layout test results

Changes affecting fewer than ~20 layout tests can be rebaselined without special coordination with the Blink gardener using these steps:

1. Prepare your Skia change, taking note of which layout tests will turn red (see http://www.chromium.org/developers/testing/webkit-layout-tests for more detail on running the Blink layout tests).
2. Check in your code to the Skia repo.
3. Ahead of the Skia auto roll including your change, manually push a change to the Blink LayoutTests/TestExpectations file, flagging tests expected to fail as a result of your change with [ NeedsManualRebaseline ].
4. Wait for the Skia roll to land successfully.
5. Check in another change to the Blink TestExpectations file changing the flags to [ NeedsRebaseline], which will prompt the automatic rebaseline.

Changes that affect a large number of test results

Where a 'large number' or 'many' means more than about 20. Follow the instructions below:

In the following the term 'code suppression' means a build flag (a.k.a. define). Such code suppressions should be given a name with the form SK_IGNORE_xxx_FIX.

There are dependency revisions which must be updated in this process. Updating a dependency revision is called a 'roll'. There are two different rolls which concern this process, each of which happens via an Auto Roll Bot multiple times per day, and can also be done manually:

• Skia roll into Chromium. See https://chromium.googlesource.com/chromium/src/+log/master/DEPS and search for skia-deps-roller.
• Blink roll into Chromium. See https://chromium.googlesource.com/chromium/src/+log/master/DEPS and search for blink-deps-roller.

Setup

Code suppression does not yet exist - Direct method

1. Make a change in Skia which will change many Blink layout tests.
2. Put the change behind a code suppression.
3. Check in the change to the Skia repository.
4. Manually roll Skia or append the autoroll with the code suppression to Chromium's 'skia/skia_common.gypi'
5. Add code suppression to Blink's 'public/blink_skia_config.gyp'.
6. Wait for Blink roll into Chromium.
7. Remove code suppression from Chromium's 'skia/skia_common.gypi'.

Code suppression does not yet exist - Alternate method

1. Add code suppression to Blink's 'public/blink_skia_config.gyp' before making code changes in Skia.
2. Make a change in Skia which will change many Blink layout tests.
3. Put the change behind a code suppression.
4. Wait for Blink roll into Chromium.
5. Check in the change to the Skia repository.
6. Wait for Skia roll into Chromium.

Code suppression exists in header

1. Remove code suppression from header file in Chromium and add code suppression to Chromium's 'skia/skia_common.gypi'. The code suppression cannot be in a header file and a defined in a gyp file at the same time or a multiple definition warning will be treated as an error and break the Chromium build.
2. Add code suppression to Blink's 'public/blink_skia_config.gyp'.
3. Wait for Blink roll into Chromium.
4. Remove code suppression from Chromium's 'skia/skia_common.gypi'.

Rebaseline

1. Choose a time when the Blink tree is likely to be quiet. Avoid PST afternoons in particular. The bigger the change, the more important this is. Regardless, determine who the Blink gardener is and notify them. You will be making the Chromium.WebKit tree very red for an extended period, and the gardener needs to know that they are not expected to fix it.
2. Create a CL removing the code suppression from Blink's public/blink_skia_config.gyp while simultaneously adding [ NeedsRebaseline ] lines to Blink's LayoutTests/TestExpectations file. Then the auto rebaseline bot will take care of the work of actually checking in the new images. This is generally acceptable for up to 600 or so rebaselined images. Above that you might still use [ NeedsRebaseline ], but it's best to coordinate with the gardener/sheriff. This should go through the CQ cleanly.
3. Be careful with tests that are already failing or flakey. These may or may not need to be rebaselined and flakey tests should not be removed from TestExpectations regardless. In such cases revert the TestExpectations changes before committing.
4. If you are not the one handling the cleanup step, please open a Skia Issue of the form Title: "Remove code suppression SK_IGNORE_xxx_FIX." Comment: "Code suppression SK_IGNORE_xxx_FIX rebaselined with Blink revision 123456." and assign it to the individual responsible for the cleanup step.

Cleanup

1. Wait for Blink roll into Chromium, so that Chromium is using the new Skia code and new Blink baselines.
2. Remove the now unused old code from Skia and any defines which were introduced to suppress the new code.
3. Check in the cleanup change to the Skia repository.
4. Wait for Skia roll into Chromium.