libbinder: writeInterfaceToken char16_t* variant

This avoids the extra allocation when we don't already have a String16
created (specifically for Java).

Bug: 169674485
Test: atest aidl_integration_test
Change-Id: I3a6344bfdc8010f07812d7d8efbbdfd2a32c7a5e
diff --git a/libs/binder/Parcel.cpp b/libs/binder/Parcel.cpp
index 19f3606..a9c19b3 100644
--- a/libs/binder/Parcel.cpp
+++ b/libs/binder/Parcel.cpp
@@ -527,14 +527,19 @@
 // Write RPC headers.  (previously just the interface token)
 status_t Parcel::writeInterfaceToken(const String16& interface)
 {
+    return writeInterfaceToken(interface.string(), interface.size());
+}
+
+status_t Parcel::writeInterfaceToken(const char16_t* str, size_t len) {
     const IPCThreadState* threadState = IPCThreadState::self();
     writeInt32(threadState->getStrictModePolicy() | STRICT_MODE_PENALTY_GATHER);
     updateWorkSourceRequestHeaderPosition();
     writeInt32(threadState->shouldPropagateWorkSource() ?
             threadState->getCallingWorkSourceUid() : IPCThreadState::kUnsetWorkSource);
     writeInt32(kHeader);
+
     // currently the interface identification token is just its name as a string
-    return writeString16(interface);
+    return writeString16(str, len);
 }
 
 bool Parcel::replaceCallingWorkSourceUid(uid_t uid)