Don't leave a discarded SharedBuffer on Resource

Don't leave a discarded SharedBuffer on Resource

If a SharedBuffer was unlocked and the OS then purged the
backing DiscardableMemory, we will evict the Resource from
MemoryCache. However, before doing so, we will give inspector
a chance to copy the data. In the case where the buffer was
purged, InspectorPageAgent may improperly handle the buffer
given its state. In that case, clear the buffer so there is
no opportunity for the inspector to misuse it.

BUG=594117
TEST=ResourceTest.LockFailureNoCrash

Committed: https://crrev.com/3c5a24bba6d4b39c5e725af9661ac0cadb1085cf
Cr-Commit-Position: refs/heads/master@{#381732}

[Nate Chapin, 2016-03-16 21:42:07]

Description was changed from

==========
Speculative fix for crbug.com/594117

BUG=
==========

to

==========
Don't leave a discarded SharedBuffer on Resource

If a SharedBuffer was unlocked and the OS then purged the
backing DiscardableMemory, we will evict the Resource from
MemoryCache. However, before doing so, we will give inspector
a chance to copy the data. In the case where the buffer was
purged, InspectorPageAgent may improperly handle the buffer
given its state. In that case, clear the buffer so there is
no opportunity for the inspector to misuse it.

BUG=594117
TEST=ResourceTest.LockFailureNoCrash
==========

[Nate Chapin, 2016-03-16 21:42:22]

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

[commit-bot: I haz the power, 2016-03-16 21:42:58]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1802313003/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1802313003/20001

[Nate Chapin, 2016-03-16 21:46:42]

japhet@chromium.org changed reviewers:
+ mkwst@chromium.org

[Nate Chapin, 2016-03-16 21:46:43]

This is fallout from https://codereview.chromium.org/1667843003

Unfortunately, I can't seem to reproduce the crash exactly in a unit test, so
I'm left testing the artifacts. A real DiscardableMemory will give a bogus data
pointer that will crash when used, while the
DiscardableMemoryImpl in base/test/test_discardable_memory_allocator.cc while
give a valid, usable one.

[commit-bot: I haz the power, 2016-03-16 23:13:34]

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

[commit-bot: I haz the power, 2016-03-16 23:13:35]

Dry run: This issue passed the CQ dry run.

[Mike West, 2016-03-17 16:21:48]

LGTM.

[Nate Chapin, 2016-03-17 16:34:26]

The CQ bit was checked by japhet@chromium.org

[commit-bot: I haz the power, 2016-03-17 16:34:36]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1802313003/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1802313003/20001

[commit-bot: I haz the power, 2016-03-17 16:44:12]

Description was changed from

==========
Don't leave a discarded SharedBuffer on Resource

If a SharedBuffer was unlocked and the OS then purged the
backing DiscardableMemory, we will evict the Resource from
MemoryCache. However, before doing so, we will give inspector
a chance to copy the data. In the case where the buffer was
purged, InspectorPageAgent may improperly handle the buffer
given its state. In that case, clear the buffer so there is
no opportunity for the inspector to misuse it.

BUG=594117
TEST=ResourceTest.LockFailureNoCrash
==========

to

==========
Don't leave a discarded SharedBuffer on Resource

If a SharedBuffer was unlocked and the OS then purged the
backing DiscardableMemory, we will evict the Resource from
MemoryCache. However, before doing so, we will give inspector
a chance to copy the data. In the case where the buffer was
purged, InspectorPageAgent may improperly handle the buffer
given its state. In that case, clear the buffer so there is
no opportunity for the inspector to misuse it.

BUG=594117
TEST=ResourceTest.LockFailureNoCrash
==========

[commit-bot: I haz the power, 2016-03-17 16:44:13]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2016-03-17 16:45:51]

Description was changed from

==========
Don't leave a discarded SharedBuffer on Resource

If a SharedBuffer was unlocked and the OS then purged the
backing DiscardableMemory, we will evict the Resource from
MemoryCache. However, before doing so, we will give inspector
a chance to copy the data. In the case where the buffer was
purged, InspectorPageAgent may improperly handle the buffer
given its state. In that case, clear the buffer so there is
no opportunity for the inspector to misuse it.

BUG=594117
TEST=ResourceTest.LockFailureNoCrash
==========

to

==========
Don't leave a discarded SharedBuffer on Resource

If a SharedBuffer was unlocked and the OS then purged the
backing DiscardableMemory, we will evict the Resource from
MemoryCache. However, before doing so, we will give inspector
a chance to copy the data. In the case where the buffer was
purged, InspectorPageAgent may improperly handle the buffer
given its state. In that case, clear the buffer so there is
no opportunity for the inspector to misuse it.

BUG=594117
TEST=ResourceTest.LockFailureNoCrash

Committed: https://crrev.com/3c5a24bba6d4b39c5e725af9661ac0cadb1085cf
Cr-Commit-Position: refs/heads/master@{#381732}
==========

[commit-bot: I haz the power, 2016-03-17 16:45:52]

Patchset 2 (id:??) landed as
https://crrev.com/3c5a24bba6d4b39c5e725af9661ac0cadb1085cf
Cr-Commit-Position: refs/heads/master@{#381732}