[remoting android] Add native library and JNI glue for host.

remoting/android/host/src/org/chromium/chromoting/host/jni/Host.java

Index: remoting/android/host/src/org/chromium/chromoting/host/jni/Host.java
diff --git a/remoting/android/host/src/org/chromium/chromoting/host/jni/Host.java b/remoting/android/host/src/org/chromium/chromoting/host/jni/Host.java
new file mode 100644
index 0000000000000000000000000000000000000000..a85adcd487f2ee243ed0cc2613d340f12217eecc
--- /dev/null
+++ b/remoting/android/host/src/org/chromium/chromoting/host/jni/Host.java
@@ -0,0 +1,44 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.chromoting.host.jni;
+
+import android.content.Context;
+
+import org.chromium.base.ContextUtils;
+import org.chromium.base.annotations.JNINamespace;
+
+/**
+ * Class to allow Java code to access the native C++ implementation of the Host process. This class
+ * controls the lifetime of the corresponding C++ object.
+ */
+@JNINamespace("remoting")
+public class Host {
+    // Pointer to the C++ object, cast to a |long|.
+    private long mNativeJniHost;
+
+    private static boolean sLoaded;
+
+    // Called once from the main Activity. Loads and initializes the native
+    // code.
+    public static void loadLibrary(Context context) {
+        if (sLoaded) return;

[Sergey Ulanov, 2016/04/07 00:41:06]

Do we need synchronization here?
Or if we don't except it to be called multiple times then this can be just an
assert.

[Lambros, 2016/04/11 18:44:47]

It's only called during Activity.onCreate() on the main thread. FindBugs hasn't
complained about it :)
AFAIK, there's nothing to prevent Android from re-using the same process for
multiple Activity onCreate()->onDestroy() lifecycles, so I think the flag is
needed.

However, if we move this to the ApplicationContext object (we create a derived
class and register it in our AndroidManifest.xml), that seems to be a true
singleton and we wouldn't need the flag:
http://stackoverflow.com/questions/11490599/can-application-context-be-change...

I'll land this as-is for now. I'll upload a separate CL to propose using the
ApplicationContext here and in the client APK.

+
+        System.loadLibrary("remoting_host_jni");
+        ContextUtils.initApplicationContext(context.getApplicationContext());
+        sLoaded = true;
+    }
+
+    public Host() {
+        mNativeJniHost = nativeInit();
+    }
+
+    private native long nativeInit();
+
+    public void destroy() {
+        nativeDestroy(mNativeJniHost);
+    }
+
+    private native void nativeDestroy(long nativeJniHost);
+}