Merge "[libutils] Modernize codebase by replacing NULL with nullptr"

libbacktrace/include/backtrace/Backtrace.h

libutils/FileMap.cpp

libutils/Looper.cpp

libutils/NativeHandle.cpp

libutils/Printer.cpp

libutils/ProcessCallStack.cpp

libutils/PropertyMap.cpp

libutils/RefBase.cpp

libutils/SharedBuffer.cpp

libutils/SharedBuffer.h

libutils/String16.cpp

libutils/String8.cpp

libutils/Threads.cpp

libutils/Timers.cpp

libutils/Tokenizer.cpp

libutils/Unicode.cpp

libutils/VectorImpl.cpp

libutils/include/utils/Condition.h

libutils/include/utils/LruCache.h

libutils/include/utils/Printer.h