[ios] Adds ScopedBlockSwizzler.

[ios] Adds ScopedBlockSwizzler.

ScopedBlockSwizzler is a helper class that swizzles methods for use in unittests
only.  It is most commonly used to inject test objects to replace shared
singletons.

BUG=662903
Committed: https://crrev.com/4aaf4523cf212b017a9d1ed6d11f6dc88544077b
Cr-Commit-Position: refs/heads/master@{#436303}

[rohitrao (ping after 24h), 2016-12-05 14:36:47]

The CQ bit was checked by rohitrao@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2016-12-05 14:36:56]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[rohitrao (ping after 24h), 2016-12-05 14:37:18]

rohitrao@chromium.org changed reviewers:
+ sdefresne@chromium.org

[commit-bot: I haz the power, 2016-12-05 15:36:15]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2016-12-05 15:36:17]

Dry run: This issue passed the CQ dry run.

[sdefresne, 2016-12-05 15:56:00]

lgtm with a question/comment (as the downstream code has the same behaviour it
is not required to fix with this CL)

https://codereview.chromium.org/2551083002/diff/1/ios/chrome/test/base/scoped...
File ios/chrome/test/base/scoped_block_swizzler.mm (right):

https://codereview.chromium.org/2551083002/diff/1/ios/chrome/test/base/scoped...
ios/chrome/test/base/scoped_block_swizzler.mm:17: IMP block_imp =
imp_implementationWithBlock(block);
The implementation requires that the block outlives the ScopedBlockSwizzler.
Maybe we can copy the block and use a ScopedBlock to keep it alive. WDYT?

[rohitrao (ping after 24h), 2016-12-05 15:58:11]

https://codereview.chromium.org/2551083002/diff/1/ios/chrome/test/base/scoped...
File ios/chrome/test/base/scoped_block_swizzler.mm (right):

https://codereview.chromium.org/2551083002/diff/1/ios/chrome/test/base/scoped...
ios/chrome/test/base/scoped_block_swizzler.mm:17: IMP block_imp =
imp_implementationWithBlock(block);
On 2016/12/05 15:56:00, sdefresne wrote:
> The implementation requires that the block outlives the ScopedBlockSwizzler.
> Maybe we can copy the block and use a ScopedBlock to keep it alive. WDYT?

Seems like a good idea, although then we'd potentially be changing the lifetime
of objects under test.  If the block captures an object and is autoreleased
after the test ends, we may unexpectedly introduce crashes (generally due to
bugs in the test).

I'll file a bug for this and we can follow up.

[rohitrao (ping after 24h), 2016-12-05 15:58:19]

The CQ bit was checked by rohitrao@chromium.org

[commit-bot: I haz the power, 2016-12-05 15:58:33]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-12-05 16:02:59]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1480953499011920, "parent_rev":
"75aaeeb1cec066ed76072fde42633e477148ab3e", "commit_rev":
"8218c0c6ecf8596fa4e025f4d696b715c8bdc885"}

[commit-bot: I haz the power, 2016-12-05 16:03:28]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-12-05 16:05:56]

Description was changed from

==========
[ios] Adds ScopedBlockSwizzler.

ScopedBlockSwizzler is a helper class that swizzles methods for use in unittests
only.  It is most commonly used to inject test objects to replace shared
singletons.

BUG=662903
==========

to

==========
[ios] Adds ScopedBlockSwizzler.

ScopedBlockSwizzler is a helper class that swizzles methods for use in unittests
only.  It is most commonly used to inject test objects to replace shared
singletons.

BUG=662903

Committed: https://crrev.com/4aaf4523cf212b017a9d1ed6d11f6dc88544077b
Cr-Commit-Position: refs/heads/master@{#436303}
==========

[commit-bot: I haz the power, 2016-12-05 16:05:57]

Patchset 1 (id:??) landed as
https://crrev.com/4aaf4523cf212b017a9d1ed6d11f6dc88544077b
Cr-Commit-Position: refs/heads/master@{#436303}