Synchronize JNI critical calls with the CC collector thread flip.

JNI critical calls (like GetArrayElementsCritical) would need to block
for the whole GC run to finish if the CC collector GC is ongoing. This
CL changes it so that they don't need to block for the GC run, but
only for the duration of the thread flip operation, which is much
shorter. This is valid due to the to-space invariant.

Bug: 12687968
Bug: 19235243

Change-Id: I1b6b4ae4fa539ddc0ec50b10ae8c8709f2a12fe8
diff --git a/runtime/thread_state.h b/runtime/thread_state.h
index a11d213..8f2f70f 100644
--- a/runtime/thread_state.h
+++ b/runtime/thread_state.h
@@ -44,6 +44,7 @@
   kWaitingForVisitObjects,          // WAITING        TS_WAIT      waiting for visiting objects
   kWaitingForGetObjectsAllocated,   // WAITING        TS_WAIT      waiting for getting the number of allocated objects
   kWaitingWeakGcRootRead,           // WAITING        TS_WAIT      waiting on the GC to read a weak root
+  kWaitingForGcThreadFlip,          // WAITING        TS_WAIT      waiting on the GC thread flip (CC collector) to finish
   kStarting,                        // NEW            TS_WAIT      native thread started, not yet ready to run managed code
   kNative,                          // RUNNABLE       TS_RUNNING   running in a JNI native method
   kSuspended,                       // RUNNABLE       TS_RUNNING   suspended by GC or debugger