This patch changes the way that the ConnectivityThread is lazily
instantiated by using the "lazy initialization holder class idiom".
The first code point that tries to obtain a reference to the unique
ConnectivityThread instance will trigger the creation of the Singleton
class, which will guarantee a thread-safe initialization of the static
INSTANCE field inside Singleton according to the language specs.
This is the Item #71 of Effective Java.
The unique static instance of ConnectivityThread is not stored directly
inside ConnectivityThread class but is stored in a static nested class.
This is to avoid triggering the creation of that unique instance when
Zygote does class preloading at phone startup. Otherwise this would lead
to Zygote creating a new OS thread during preloading, which is a fatal
error.
Test: frameworks-wifi tests pass
Bug: 26749700
Bug: 28537383
Bug: 32130437
(cherry picked from commit 3ab84b087a)
(cherry picked from commit 8f201294fe)
Change-Id: Ic9a31809ef19e618246f9aa17f5df29bd65f8510
e4f69293e9