Use nullptr instead of reinterpret_cast of NULL to pointer type am: d524f97614 am: e079d61912 am: e9ddf7d93d

Original change: https://android-review.googlesource.com/c/platform/external/libchrome/+/1972019

Change-Id: I2efc80b1d1cee60f3282e12b9e7fa2f143f1fbee