fix race condition between HWUI cache and renderThread

getMaximumBitmapWidth() and getMaximumBitmapHeight() of DisplayListCanvas
need HWUI cache instance. Since the initialization of the cache is
asynchronous it may crash if not yet ready. Add a staticFence() call
to guarantee the cache has been created prior issuing the call.

Change-Id: I5ed9e5cc084444c8d1872a77fef50e294ae14e93
Signed-off-by: Thomas Buhot <thomas.buhot@intel.com>
Signed-off-by: Zhiquan Liu <zhiquan.liu@intel.com>