[Device Service] Decouple NFC implementation from //content

content/public/android/java/src/org/chromium/content/browser/NfcHost.java

Index: content/public/android/java/src/org/chromium/content/browser/NfcHost.java
diff --git a/content/public/android/java/src/org/chromium/content/browser/NfcHost.java b/content/public/android/java/src/org/chromium/content/browser/NfcHost.java
new file mode 100644
index 0000000000000000000000000000000000000000..fd6096bb90f4508b783b503f74659d5147fc7f7c
--- /dev/null
+++ b/content/public/android/java/src/org/chromium/content/browser/NfcHost.java
@@ -0,0 +1,104 @@
+// 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.content.browser;
+
+import android.app.Activity;
+import android.util.SparseArray;
+
+import org.chromium.base.Callback;
+import org.chromium.base.annotations.CalledByNative;
+import org.chromium.content_public.browser.WebContents;
+import org.chromium.content_public.browser.WebContentsObserver;
+import org.chromium.ui.base.WindowAndroid;
+
+/**
+ * Tracks the Activiy for a given WebContents on behalf of a NFC instance that
+ * cannot talk directly to WebContents.
+ */
+class NfcHost extends WebContentsObserver implements WindowAndroidChangedObserver {
+    // The WebContents with which this host is associated.
+    private WebContents mWebContents;
+    private ContentViewCore mContentViewCore;
+
+    // The callback that the NFC instance has registered for being notified
+    // when the Activity changes.
+    private Callback<Activity> mCallback;
+
+    // The context ID with which this host is associated.
+    private int mContextId;
+
+    private static final SparseArray<NfcHost> mContextHostsMap = new SparseArray<NfcHost>();
+
+    /**
+     * Provides access to NfcHost via context ID.
+     */
+    public static NfcHost fromContextId(int contextId) {
+        return mContextHostsMap.get(contextId);
+    }
+
+    @CalledByNative
+    private static NfcHost create(WebContents webContents, int contextId) {
+        return new NfcHost(webContents, contextId);
+    }
+
+    NfcHost(WebContents webContents, int contextId) {
+        mCallback = null;
+        mWebContents = webContents;
+        mContentViewCore = ContentViewCore.fromWebContents(mWebContents);
+        mContextId = contextId;
+        mContextHostsMap.put(mContextId, this);
+    }
+
+    /** Called by the NFC implementation (via ContentNfcDelegate) to allow
+     * that implementation to track changes to the Activity associated with
+     * its context ID (i.e., the activity associated with |mWebContents|).
+     */
+    public void trackActivityChanges(Callback<Activity> callback) {
+        // Only the main frame is allowed to access NFC
+        // (https://w3c.github.io/web-nfc/#security-policies). The renderer
+        // enforces this by dropping connection requests from nested frames.
+        // Therefore, this class should never see a request to track activity
+        // changes while there is already such a request.
+        assert mCallback == null : "Unexpected request to track activity changes";
+        mCallback = callback;
+        Activity activity = null;
+
+        if (mContentViewCore != null) {
+            mContentViewCore.addWindowAndroidChangedObserver(this);
+            if (mContentViewCore.getWindowAndroid() != null) {
+                activity = mContentViewCore.getWindowAndroid().getActivity().get();
+            }
+        }
+
+        mCallback.onResult(activity);
+    }
+
+    public void stopTrackingActivityChanges() {
+        mCallback = null;
+        if (mContentViewCore != null) {
+            mContentViewCore.removeWindowAndroidChangedObserver(this);
+        }
+    }
+
+    @Override
+    public void destroy() {
+        mContextHostsMap.remove(mContextId);
+        mCallback = null;
+        if (mContentViewCore != null) {
+            mContentViewCore.removeWindowAndroidChangedObserver(this);
+        }
+        super.destroy();
+    }
+
+    @Override
+    public void onWindowAndroidChanged(WindowAndroid newWindowAndroid) {
+        Activity activity = null;
+        if (newWindowAndroid != null) {
+            activity = newWindowAndroid.getActivity().get();
+        }
+        assert mCallback != null : "should have callback";
+        mCallback.onResult(activity);
+    }
+}