content: Add DeletedDiscardableSharedMemory IPC.

content: Add DeletedDiscardableSharedMemory IPC.

This provides a mechanism for child processes to notify the
browser process that a discardable memory segment has been
deleted. This reduces the chance of the browser unnecessarily
purging a memory segment that is still useful and it makes
total discardable memory usage stats in the browser process
better match current usage by all child processes.

BUG=
TEST=content_unittests --gtest_filter=DiscardableSharedMemoryHeapTest.DeletedCallback, content_browsertests --gtest_filter=ChildDiscardableSharedMemoryManagerBrowserTest.ReleaseFreeMemory

Committed: https://crrev.com/1500e1a7a2445bb9bddc9e492db6c988dfbc815f
Cr-Commit-Position: refs/heads/master@{#320848}

[reveman, 2015-03-16 13:03:17]

reveman@chromium.org changed reviewers:
+ avi@chromium.org

[Avi (use Gerrit), 2015-03-16 16:58:21]

https://codereview.chromium.org/1009203004/diff/20001/content/common/host_dis...
File content/common/host_discardable_shared_memory_manager.h (right):

https://codereview.chromium.org/1009203004/diff/20001/content/common/host_dis...
content/common/host_discardable_shared_memory_manager.h:22: typedef int32
DiscardableSharedMemoryId;
First, int32_t, per the deprecation notice in base/basictypes.h. Second, why not
make this a class member:?

[reveman, 2015-03-16 18:30:55]

https://codereview.chromium.org/1009203004/diff/20001/content/common/host_dis...
File content/common/host_discardable_shared_memory_manager.h (right):

https://codereview.chromium.org/1009203004/diff/20001/content/common/host_dis...
content/common/host_discardable_shared_memory_manager.h:22: typedef int32
DiscardableSharedMemoryId;
On 2015/03/16 16:58:21, Avi wrote:
> First, int32_t, per the deprecation notice in base/basictypes.h. Second, why
not
> make this a class member:?

int32 -> int32_t, Done.

The reason I didn't make it a class member is because it's shared between
ChildDiscardableSharedMemoryManager and this Host class. I think it would be
more correct to move this into it's own header
(content/common/discardable_shared_memory_id.h) and keep the
DiscardableSharedMemoryId name but that felt overkill for a simple typedef.
Another option is to just get rid of it and instead use 'int32_t' everywhere.
Let me know what you think is best.

[Avi (use Gerrit), 2015-03-16 19:11:44]

On 2015/03/16 18:30:55, reveman wrote:
>
https://codereview.chromium.org/1009203004/diff/20001/content/common/host_dis...
> File content/common/host_discardable_shared_memory_manager.h (right):
> 
>
https://codereview.chromium.org/1009203004/diff/20001/content/common/host_dis...
> content/common/host_discardable_shared_memory_manager.h:22: typedef int32
> DiscardableSharedMemoryId;
> On 2015/03/16 16:58:21, Avi wrote:
> > First, int32_t, per the deprecation notice in base/basictypes.h. Second, why
> not
> > make this a class member:?
> 
> int32 -> int32_t, Done.
> 
> The reason I didn't make it a class member is because it's shared between
> ChildDiscardableSharedMemoryManager and this Host class. I think it would be
> more correct to move this into it's own header
> (content/common/discardable_shared_memory_id.h) and keep the
> DiscardableSharedMemoryId name but that felt overkill for a simple typedef.
> Another option is to just get rid of it and instead use 'int32_t' everywhere.
> Let me know what you think is best.

That makes sense. Let's leave it as a top-level typedef then.

[reveman, 2015-03-16 21:56:33]

reveman@chromium.org changed reviewers:
+ nasko@chromium.org

[reveman, 2015-03-16 21:56:33]

+nasko for content/common/child_process_messages.h

avi, does latest patch look ok?

[Avi (use Gerrit), 2015-03-16 22:51:11]

On 2015/03/16 21:56:33, reveman wrote:
> +nasko for content/common/child_process_messages.h
> 
> avi, does latest patch look ok?

Forgot to lgtm

[nasko, 2015-03-16 23:02:49]

IPC LGTM

[reveman, 2015-03-16 23:46:37]

The CQ bit was checked by reveman@chromium.org

[commit-bot: I haz the power, 2015-03-16 23:46:58]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1009203004/60001

[commit-bot: I haz the power, 2015-03-17 02:31:48]

Committed patchset #4 (id:60001)

[commit-bot: I haz the power, 2015-03-17 02:32:24]

Patchset 4 (id:??) landed as
https://crrev.com/1500e1a7a2445bb9bddc9e492db6c988dfbc815f
Cr-Commit-Position: refs/heads/master@{#320848}