Fix ImportDataHandler crash.

Fix ImportDataHandler crash.

The same ImportDataHandler lives throughout the browser process and handles all imports.

The following could thus result in derefing a NULL pointer:
1) Importer1 launches (and importer_host_ is set to it)
2) Importer2 launches (and importer_host_ is set to it)
3) Importer2 is done and notifies us via ImportEnded
4) This results in us setting importer_host_ = NULL;
5) Importer1 is done and notifies us via ImportEnded
6) This result in us calling importer_host_->set_observer(NULL); when importer_host_ is NULL

This CL makes it so that on a new import request if importer_host_ is not NULL we do importer_host_->set_observer(NULL) in order to let the ongoing import finish silently without bothering us when it's done.

The current UI is such that it is possible to spam-click the import button and generate multiple identical imports; perhaps this should be fixed, but as a fix for M30 I think this is the simplest we can do.

This problem was also present in another method added in http://crrev.com/216947; moved some code around to fix both issues at once.

BUG=292791
TEST=Repro steps @ https://code.google.com/p/chromium/issues/detail?id=292791#c4 no longer result in crash.
R=estade@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=223933

[gab, 2013-09-17 22:50:30]

Evan, please take a look.

Thanks!
Gab

[Evan Stade, 2013-09-17 23:20:09]

lgtm

https://chromiumcodereview.appspot.com/24195005/diff/1/chrome/browser/ui/webu...
File chrome/browser/ui/webui/options/import_data_handler.cc (right):

https://chromiumcodereview.appspot.com/24195005/diff/1/chrome/browser/ui/webu...
chrome/browser/ui/webui/options/import_data_handler.cc:220: void* /* params */)
{
nit: int /*index*/

(no spaces around var name)

[gab, 2013-09-18 14:32:35]

Thanks!

https://chromiumcodereview.appspot.com/24195005/diff/1/chrome/browser/ui/webu...
File chrome/browser/ui/webui/options/import_data_handler.cc (right):

https://chromiumcodereview.appspot.com/24195005/diff/1/chrome/browser/ui/webu...
chrome/browser/ui/webui/options/import_data_handler.cc:220: void* /* params */)
{
On 2013/09/17 23:20:10, Evan Stade wrote:
> nit: int /*index*/
> 
> (no spaces around var name)

Done.

[commit-bot: I haz the power, 2013-09-18 14:33:02]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/gab@chromium.org/24195005/7001

[gab, 2013-09-18 20:37:38]

Committed patchset #2 manually as r223933 (presubmit successful).