libbinder: support inheriting realtime priority

gotta go fast

Bug: 170420170
Test: atest binderLibTest
Change-Id: I2f2c6cb35ebf463d90b517e134b9ea3114764af6
diff --git a/libs/binder/Binder.cpp b/libs/binder/Binder.cpp
index f2d223d..d964d25 100644
--- a/libs/binder/Binder.cpp
+++ b/libs/binder/Binder.cpp
@@ -133,6 +133,7 @@
 public:
     // unlocked objects
     bool mRequestingSid = false;
+    bool mInheritRt = false;
     sp<IBinder> mExtension;
     int mPolicy = SCHED_NORMAL;
     int mPriority = 0;
@@ -327,6 +328,27 @@
     return e->mPriority;
 }
 
+bool BBinder::isInheritRt() {
+    Extras* e = mExtras.load(std::memory_order_acquire);
+
+    return e && e->mInheritRt;
+}
+
+void BBinder::setInheritRt(bool inheritRt) {
+    Extras* e = mExtras.load(std::memory_order_acquire);
+
+    if (!e) {
+        if (!inheritRt) {
+            return;
+        }
+
+        e = getOrCreateExtras();
+        if (!e) return; // out of memory
+    }
+
+    e->mInheritRt = inheritRt;
+}
+
 pid_t BBinder::getDebugPid() {
     return getpid();
 }