When an attribute value is missing, we can immediately return the
default value instead of paying the cost of throwing an exception.
To bring this benefit to both human-readable and binary XML, this
is implemented by adding a new getAttributeIndex() lookup method
which is then used by default methods.
readExtraAttributes() also appears to be parsing a string list as
a boolean value (which seems very broken), so we add hand-rolled
parsing logic to avoid paying the cost of an exception. Someone
should follow up in the future to investigate if there's an actual
bug here.
Bug: 174544002
Test: manual
Change-Id: Id313d18000e345ca1acd3c66d2c0c0fc44769b71
78e84716e6