Make dragging apps out of the app launcher work for aura.

This also makes it so that the dragged icon doesn't grow
when picked up, as the win32 API for dragging only supports
a fixed size image for its drag icon.

BUG=308758

Review URL: https://codereview.chromium.org/65953003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238024 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238024
Let test_isolation_mode default to check on mac.

It was set to noop in https://chromiumcodereview.appspot.com/14055005 due to
issues with xcode. Now that xcode is no longer used, it can be set to check
again.

BUG=none

Review URL: https://codereview.chromium.org/92303002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238025 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238025