Reduce the scope of CheckJNI.

CheckJNI wasn't anonymous so that it could friend JniEnvExt. Add
accessors for the CheckJNI parts of JniEnvExt and make CheckJNI and
related classes anonymous. This is equivalent to making functions
within the scope of a file static and preferred now by cppstyle.
Make the force_copy_ field that could be const, const.
Test: m -j32; booted emulator.

Change-Id: I7e740d3b9bf4a3fedd30c4f44a852af67898d2f0
3 files changed