Fix constructor parameters shadowing member variables

Using the same name for the constructor parameter and the member
variable causes a warning that was being hidden by the use of -isystem
to include frameworks/native/include.  Prefix the parameter with an
underscore.

Bug: 31752268
Test: m -j
Change-Id: I7748934f1e9515176e2ae98d2c0e58d165a7a5c2