Allow a GLThread to release and reacquire the EGL Surface as needed.

We currently only allow one GLThread to have an active EGL Surface at a
time.(This may be lifted in the future, when EGL and GL are reentrant.)

Prior to this change we would enforce this rule by having older GLThreads
quit when a new GLThread started. That had the drawback of leaving the
older GLSurfaceViews in a zombie state -- their GLThreads would be
gone.

We now enforce this rule by just releasing and reacquiring the EGL surface
context as needed.

Specific changes to the code:

created private helper methods - startEgl and stopEgl to help manage
starting and stopping EGL.

Move the calls to sGLThreadManager start and end from the outermost run
method into the startEgl / stopEgl methods.

Reworked the wait loop to handle starting and stopping EGL as needed.

needToWait() gets simpler -- just looks at current status.

sGLThreadManager.shouldQuit was replaced by shouldHaveEgl.


This is another step in fixing bug 2228262.