[rAC, OSX] Force better initial size for sign-in (2nd try)

This is a re-land of http://crrev.com/103853004 (r240566), which was
reverted in http://crrev.com/113913008 (r240603)

The revert was due to a test failure with the root cause that
AutofillDialogBrowserTest shows the dialog, but never runs the
NSRunLoop - which means the visual display is not fully updated. And
showing the sign-in dialog requires the main dialog's size to be non-
zero.

Fixes added:
* AutofillSignInDelegate DCHECKs for invalid sizes (better callstacks)
* AutofillDialogBrowserTest cycles run loops whenever dialog is shown

---- original description ----
Open the sign-in dialog with an initial size equal to the current
dialog. This avoids one unnecessary resize until the content is loaded
and makes the visual experience less jarring.
---- end original description ----

TBR=jochen@chromium.org
R=isherman@chromium.org
BUG=325518

Review URL: https://codereview.chromium.org/97993006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@241009 0039d316-1c4b-4281-b951-d872f2087c98
Getting rid of GetDefaultProfile & fixing multi user issues with accessibility

As discussed: I removed the occurances, switched the accessibility functionality with a user change and made sure that the accessibility menu is presented when at least one user has one accessibility feature turned on.

Not done:
- ChromeVox - this will most likely only partially work in multi user scenarios. It makes no sense to get this 80% working if we are in the midst of overhauling the use of ChromeVox. This needs to be re-visited once the changes are done.
- BrailleDisplayAPI - Since this is coupled with ChromeVox I guess that this falls into the same problem.
- MagnifierManager - A refactor should be done which merges this into the AccessibilityManager, but that would go beyond what we currently have to do. Besides I have found a comment which indicates that this might even be underway.


BUG=322682
TEST=unit tests (and multi profile by visual tests)

Review URL: https://codereview.chromium.org/102483006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@241010 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 241010
Adds update detection to DnsSdRegistry, so that notifications from the service watcher that don't result in changes to the contents of the registry don't result in chrome.mdns events.

BUG=328133

Review URL: https://codereview.chromium.org/114673004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@241013 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 241013