WebUI TaskManager: make it default on Chrome OS

WebUI TaskManager: make it default on Chrome OS 

And fixes the code of task manager and following tests which didn't work correctly on WebUI TaskManager.
- TaskManagerBrowserTest.ShutdownWhileOpen
- ExtensionApiTest.ProcessesVsTaskManager
- PrerenderBrowserTest.PrerenderTaskManager


BUG=chromium-os:13885
TEST=trybots

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=95015

[xiyuan, 2011-07-29 18:04:56]

LGTM with nits

http://codereview.chromium.org/7520011/diff/1/chrome/browser/task_manager/tas...
File chrome/browser/task_manager/task_manager_browsertest_util.h (right):

http://codereview.chromium.org/7520011/diff/1/chrome/browser/task_manager/tas...
chrome/browser/task_manager/task_manager_browsertest_util.h:21: class
ResourceChangeObserver : public TaskManagerModelObserver {
nit: Is ResourceChangeObserver used anywhere else? If not, suggest to move it to
a cc file.

http://codereview.chromium.org/7520011/diff/1/chrome/browser/task_manager/tas...
chrome/browser/task_manager/task_manager_browsertest_util.h:29: virtual void
OnModelChanged() {
nit: OVERRIDE and other virtual functions below.

http://codereview.chromium.org/7520011/diff/1/chrome/browser/task_manager/tas...
chrome/browser/task_manager/task_manager_browsertest_util.h:56: class
TaskManagerReadyListener : public NotificationObserver {
nit: If TaskManagerReadyListener not used anywhere else, suggest to move it inot
a cc file.

http://codereview.chromium.org/7520011/diff/1/chrome/browser/task_manager/tas...
chrome/browser/task_manager/task_manager_browsertest_util.h:61: LOG(ERROR) <<
"added";
nit: remove this LOG or fix indentation

http://codereview.chromium.org/7520011/diff/1/chrome/browser/task_manager/tas...
chrome/browser/task_manager/task_manager_browsertest_util.h:63: virtual void
Observe(int type,
nit: insert an empty line before

http://codereview.chromium.org/7520011/diff/1/chrome/browser/task_manager/tas...
chrome/browser/task_manager/task_manager_browsertest_util.h:69: LOG(ERROR) <<
"Observed";
nit: remove this LOG or fix the indentation.

http://codereview.chromium.org/7520011/diff/1/chrome/browser/task_manager/tas...
chrome/browser/task_manager/task_manager_browsertest_util.h:82: virtual void
Observe(int type,
nit: insert an empty line before

[mazda, 2011-07-29 18:20:37]

LGTM with a nit

http://codereview.chromium.org/7520011/diff/1/chrome/browser/task_manager/tas...
File chrome/browser/task_manager/task_manager_browsertest_util.h (right):

http://codereview.chromium.org/7520011/diff/1/chrome/browser/task_manager/tas...
chrome/browser/task_manager/task_manager_browsertest_util.h:131: 
redundant line?