Transfer v8 snapshot files as file descriptors to child processes on Posix

Transfer v8 snapshot files as file descriptors to child processes on Posix.

An update on Chrome could replace the V8 snapshot files with newer version.
For zygoted processes this is OK because the zygote will have already mapped
the V8 snapshot and thus child processes will use the correct version of the
snapshot.  However, for processes which don't use the zygote (such as
unsandboxed plugin processes) base::LaunchProcess will launch the old
version of he Chrome binary (via /proc/self/exe on Linux), but the child will
read the new version of the V8 snapshot, thus causing a crash due to a
version mismatch.

The fix is to load V8 snapshot file in the browser and pass a file descriptor to
the child processes (much like Android already did, but for different reasons).
This ensures that the child process always sees the correct version of the
snapshot file.

BUG=457656, 461057
Committed: https://crrev.com/3fb072718b5ff38aa9c34d8d5160404aa2ad50a5
Cr-Commit-Position: refs/heads/master@{#317790}

[rmcilroy, 2015-02-20 22:50:40]

rmcilroy@chromium.org changed reviewers:
+ jochen@chromium.org

[rmcilroy, 2015-02-20 22:50:41]

Jochen: could you take a look please? Thanks.

[rmcilroy, 2015-02-20 22:53:25]

https://codereview.chromium.org/944913002/diff/40001/content/shell/browser/sh...
File content/shell/browser/shell_content_browser_client.cc (right):

https://codereview.chromium.org/944913002/diff/40001/content/shell/browser/sh...
content/shell/browser/shell_content_browser_client.cc:345:
mappings->Share(kV8SnapshotDataDescriptor, v8_snapshot_fd_.get());
I'm not keen on the duplication with chrome_content_browser_client here, but
there doesn't seem to be a convenient common class and existing code already
seems to duplicate between these classes.  Let me know if you have an
alternative.

[jochen (gone - plz use gerrit), 2015-02-23 12:12:27]

why is this not possible on mac as well?

[rmcilroy, 2015-02-23 12:27:52]

On 2015/02/23 12:12:27, jochen (slow) wrote:
> why is this not possible on mac as well?

Mac doesn't define GetAdditionalMappedFilesForChildProcess() - I'm not sure if
there is some reason why it doesn't or if it just hasn't needed to before,
however there are various subtleties of the Mac launch process which are
different and we've not seen this issue on Mac yet so I prefered to keep this
focused on Linux.

[jochen (gone - plz use gerrit), 2015-02-23 12:32:36]

ok, could you file a bug that mac/win should switch to this model as well?

lgtm then

[rmcilroy, 2015-02-23 22:10:10]

On 2015/02/23 12:32:36, jochen (slow) wrote:
> ok, could you file a bug that mac/win should switch to this model as well?
> 
> lgtm then

Filed a bug at crbug.com/461057.  Also had to make a few more changes to fix
Android webview and content_browsertests.  PTAL, thanks.

[jochen (gone - plz use gerrit), 2015-02-24 09:33:37]

lgtm

[rmcilroy, 2015-02-24 09:40:00]

The CQ bit was checked by rmcilroy@chromium.org

[commit-bot: I haz the power, 2015-02-24 09:41:28]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/944913002/80001

[commit-bot: I haz the power, 2015-02-24 10:02:19]

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

[commit-bot: I haz the power, 2015-02-24 10:02:20]

Try jobs failed on following builders:
  ios_rel_device_ninja_ng on tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_rel_device_ni...)

[rmcilroy, 2015-02-24 12:02:17]

The CQ bit was checked by rmcilroy@chromium.org

[rmcilroy, 2015-02-24 12:02:17]

The patchset sent to the CQ was uploaded after l-g-t-m from jochen@chromium.org
Link to the patchset: https://codereview.chromium.org/944913002/#ps100001
(title: "Fix iOS")

[commit-bot: I haz the power, 2015-02-24 12:02:50]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/944913002/100001

[commit-bot: I haz the power, 2015-02-24 13:33:12]

Committed patchset #6 (id:100001)

[commit-bot: I haz the power, 2015-02-24 13:33:59]

Patchset 6 (id:??) landed as
https://crrev.com/3fb072718b5ff38aa9c34d8d5160404aa2ad50a5
Cr-Commit-Position: refs/heads/master@{#317790}