[android] Disable 3 failing accessibility-related content browsertests.

DumpAccessibilityTreeTest.AccessibilityDialog
DumpAccessibilityTreeTest.AccessibilityModalDialogClosed
DumpAccessibilityTreeTest.AccessibilityModalDialogInIframeOpened

BUG=297230
TBR=dmazzoni@chromium.org
NOTRY=True

Review URL: https://codereview.chromium.org/68983006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@235740 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 235740