Add the -Xcheck:jni option.

And make sure the boolean is available in every JNIEnv, so we
don't have to look it up via Runtime and JavaVM every time we
need to use it.

Change-Id: I2d4b5d04ded196e7c7602406d854bb35227d767a
diff --git a/src/jni_internal.cc b/src/jni_internal.cc
index e23b162..1be9d76 100644
--- a/src/jni_internal.cc
+++ b/src/jni_internal.cc
@@ -2037,9 +2037,10 @@
 static const size_t kMonitorTableInitialSize = 32; // Arbitrary.
 static const size_t kMonitorTableMaxSize = 4096; // Arbitrary sanity check.
 
-JNIEnvExt::JNIEnvExt(Thread* self)
+JNIEnvExt::JNIEnvExt(Thread* self, bool check_jni)
     : fns(&gNativeInterface),
       self(self),
+      check_jni(check_jni),
       critical(false),
       monitor_table("monitor table", kMonitorTableInitialSize, kMonitorTableMaxSize) {
   // TODO: kill these.
@@ -2179,9 +2180,10 @@
 static const size_t kPinTableInitialSize = 16;
 static const size_t kPinTableMaxSize = 1024;
 
-JavaVMExt::JavaVMExt(Runtime* runtime)
+JavaVMExt::JavaVMExt(Runtime* runtime, bool check_jni)
     : fns(&gInvokeInterface),
       runtime(runtime),
+      check_jni(check_jni),
       pin_table("pin table", kPinTableInitialSize, kPinTableMaxSize) {
 }