[Android WebView] Implement AwContentsLifecycleNotifier.

This patch provides a way to observe webview lifecycle on the java
side. By implementing AwContentsLifecycleNotifier.Observer and
registering with the notifier, clients will get notified when there
are alive instances of webviews (i.e. aw_contents) or when all
webview instances have been destroyed.

This is useful for APIs which can be disabled when there are no
living webviews, e.g. Network Information API.

BUG=520088

Review URL: https://codereview.chromium.org/1419083010

Cr-Commit-Position: refs/heads/master@{#362706}

8 files changed, 197 insertions, 0 deletions

diff --git a/android_webview/java/src/org/chromium/android_webview/AwContentsLifecycleNotifier.java b/android_webview/java/src/org/chromium/android_webview/AwContentsLifecycleNotifier.java
new file mode 100644
index 0000000..6701c95
--- /dev/null
+++ b/android_webview/java/src/org/chromium/android_webview/AwContentsLifecycleNotifier.java
@@ -0,0 +1,74 @@
+// Copyright 2015 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.android_webview;
+
+import org.chromium.base.ObserverList;
+import org.chromium.base.ThreadUtils;
+import org.chromium.base.annotations.CalledByNative;
+import org.chromium.base.annotations.JNINamespace;
+
+/**
+ * This class is intended to notify observers of the existence native instances of
+ * aw_contents. It receives a callback when native aw_contents are created or
+ * destroyed. Observers are notified when the first instance is created or the
+ * last instance is destroyed.
+ */
+@JNINamespace("android_webview")
+public class AwContentsLifecycleNotifier {
+
+    /**
+     * Observer interface to be implemented by deriving webview lifecycle observers.
+     */
+    public static interface Observer {
+        public void onFirstWebViewCreated();
+        public void onLastWebViewDestroyed();
+    }
+
+    private static final ObserverList<Observer> sLifecycleObservers =
+            new ObserverList<Observer>();
+    private static int sNumWebViews = 0;
+
+    private AwContentsLifecycleNotifier() {}
+
+    public static void addObserver(Observer observer) {
+        sLifecycleObservers.addObserver(observer);
+    }
+
+    public static void removeObserver(Observer observer) {
+        sLifecycleObservers.removeObserver(observer);
+    }
+
+    public static boolean hasWebViewInstances() {
+        return sNumWebViews > 0;
+    }
+
+    // Called on UI thread.
+    @CalledByNative
+    private static void onWebViewCreated() {
+        ThreadUtils.assertOnUiThread();
+        assert sNumWebViews >= 0;
+        sNumWebViews++;
+        if (sNumWebViews == 1) {
+            // first webview created, notify observers.
+            for (Observer observer : sLifecycleObservers) {
+                observer.onFirstWebViewCreated();
+            }
+        }
+    }
+
+    // Called on UI thread.
+    @CalledByNative
+    private static void onWebViewDestroyed() {
+        ThreadUtils.assertOnUiThread();
+        assert sNumWebViews > 0;
+        sNumWebViews--;
+        if (sNumWebViews == 0) {
+            // last webview destroyed, notify observers.
+            for (Observer observer : sLifecycleObservers) {
+                observer.onLastWebViewDestroyed();
+            }
+        }
+    }
+}
diff --git a/android_webview/javatests/src/org/chromium/android_webview/test/AwContentsLifecycleNotifierTest.java b/android_webview/javatests/src/org/chromium/android_webview/test/AwContentsLifecycleNotifierTest.java
new file mode 100644
index 0000000..2c7d408
--- /dev/null
+++ b/android_webview/javatests/src/org/chromium/android_webview/test/AwContentsLifecycleNotifierTest.java
@@ -0,0 +1,57 @@
+// Copyright 2015 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.android_webview.test;
+
+import android.test.suitebuilder.annotation.SmallTest;
+
+import org.chromium.android_webview.AwContentsLifecycleNotifier;
+import org.chromium.base.test.util.Feature;
+import org.chromium.content.browser.test.util.CallbackHelper;
+
+/**
+ * AwContentsLifecycleNotifier tests.
+ */
+public class AwContentsLifecycleNotifierTest extends AwTestBase {
+
+    private TestAwContentsClient mContentsClient = new TestAwContentsClient();
+
+    private static class LifecycleObserver implements AwContentsLifecycleNotifier.Observer {
+        public CallbackHelper mFirstWebViewCreatedCallback = new CallbackHelper();
+        public CallbackHelper mLastWebViewDestroyedCallback = new CallbackHelper();
+
+        @Override
+        public void onFirstWebViewCreated() {
+            mFirstWebViewCreatedCallback.notifyCalled();
+        }
+
+        @Override
+        public void onLastWebViewDestroyed() {
+            mLastWebViewDestroyedCallback.notifyCalled();
+        }
+    }
+
+    @SmallTest
+    @Feature({"AndroidWebView"})
+    public void testNotifierCreate() throws Throwable {
+        LifecycleObserver observer = new LifecycleObserver();
+        AwContentsLifecycleNotifier.addObserver(observer);
+        assertFalse(AwContentsLifecycleNotifier.hasWebViewInstances());
+
+        AwTestContainerView awTestContainerView =
+                createAwTestContainerViewOnMainSync(mContentsClient);
+        observer.mFirstWebViewCreatedCallback.waitForCallback(0, 1);
+        assertTrue(AwContentsLifecycleNotifier.hasWebViewInstances());
+
+        getInstrumentation().runOnMainSync(new Runnable() {
+            @Override
+            public void run() {
+                getActivity().removeAllViews();
+            }
+        });
+        destroyAwContentsOnMainSync(awTestContainerView.getAwContents());
+        observer.mLastWebViewDestroyedCallback.waitForCallback(0, 1);
+        assertFalse(AwContentsLifecycleNotifier.hasWebViewInstances());
+    }
+}
diff --git a/android_webview/native/BUILD.gn b/android_webview/native/BUILD.gn
index 320cbb3..cec2c0e 100644
--- a/android_webview/native/BUILD.gn
+++ b/android_webview/native/BUILD.gn
@@ -47,6 +47,8 @@ source_set("native") {
     "aw_contents_client_bridge.h",
     "aw_contents_io_thread_client_impl.cc",
     "aw_contents_io_thread_client_impl.h",
+    "aw_contents_lifecycle_notifier.cc",
+    "aw_contents_lifecycle_notifier.h",
     "aw_contents_statics.cc",
     "aw_contents_statics.h",
     "aw_debug.cc",
@@ -118,6 +120,7 @@ generate_jni("native_jni") {
     "../java/src/org/chromium/android_webview/AwContentsBackgroundThreadClient.java",
     "../java/src/org/chromium/android_webview/AwContentsClientBridge.java",
     "../java/src/org/chromium/android_webview/AwContentsIoThreadClient.java",
+    "../java/src/org/chromium/android_webview/AwContentsLifecycleNotifier.java",
     "../java/src/org/chromium/android_webview/AwContentsStatics.java",
     "../java/src/org/chromium/android_webview/AwCookieManager.java",
     "../java/src/org/chromium/android_webview/AwDebug.java",
diff --git a/android_webview/native/android_webview_jni_registrar.cc b/android_webview/native/android_webview_jni_registrar.cc
index 275e29b..a585d7e 100644
--- a/android_webview/native/android_webview_jni_registrar.cc
+++ b/android_webview/native/android_webview_jni_registrar.cc
@@ -10,6 +10,7 @@
 #include "android_webview/native/aw_contents_background_thread_client.h"
 #include "android_webview/native/aw_contents_client_bridge.h"
 #include "android_webview/native/aw_contents_io_thread_client_impl.h"
+#include "android_webview/native/aw_contents_lifecycle_notifier.h"
 #include "android_webview/native/aw_contents_statics.h"
 #include "android_webview/native/aw_debug.h"
 #include "android_webview/native/aw_dev_tools_server.h"
@@ -59,6 +60,7 @@ static base::android::RegistrationMethod kWebViewRegisteredMethods[] = {
   { "InputStream", RegisterInputStream },
   { "JavaBrowserViewRendererHelper", RegisterJavaBrowserViewRendererHelper },
   { "AwMessagePortService", RegisterAwMessagePortService },
+  { "AwContentsLifecycleNotifier", RegisterAwContentsLifecycleNotifier },
 };
 
 bool RegisterJni(JNIEnv* env) {
diff --git a/android_webview/native/aw_contents.cc b/android_webview/native/aw_contents.cc
index 4a829fa..8ec6260 100644
--- a/android_webview/native/aw_contents.cc
+++ b/android_webview/native/aw_contents.cc
@@ -22,6 +22,7 @@
 #include "android_webview/native/aw_browser_dependency_factory.h"
 #include "android_webview/native/aw_contents_client_bridge.h"
 #include "android_webview/native/aw_contents_io_thread_client_impl.h"
+#include "android_webview/native/aw_contents_lifecycle_notifier.h"
 #include "android_webview/native/aw_message_port_service_impl.h"
 #include "android_webview/native/aw_pdf_exporter.h"
 #include "android_webview/native/aw_picture.h"
@@ -209,6 +210,7 @@ AwContents::AwContents(scoped_ptr<WebContents> web_contents)
     InitAutofillIfNecessary(autofill_manager_delegate->GetSaveFormData());
   content::SynchronousCompositor::SetClientForWebContents(
       web_contents_.get(), &browser_view_renderer_);
+  AwContentsLifecycleNotifier::OnWebViewCreated();
 }
 
 void AwContents::SetJavaPeers(JNIEnv* env,
@@ -293,9 +295,12 @@ AwContents::~AwContents() {
   // Chromium, because the app process may continue to run for a long time
   // without ever using another WebView.
   if (instance_count == 0) {
+    // TODO(timvolodine): consider moving NotifyMemoryPressure to
+    // AwContentsLifecycleNotifier (crbug.com/522988).
     base::MemoryPressureListener::NotifyMemoryPressure(
         base::MemoryPressureListener::MEMORY_PRESSURE_LEVEL_CRITICAL);
   }
+  AwContentsLifecycleNotifier::OnWebViewDestroyed();
 }
 
 base::android::ScopedJavaLocalRef<jobject>
diff --git a/android_webview/native/aw_contents_lifecycle_notifier.cc b/android_webview/native/aw_contents_lifecycle_notifier.cc
new file mode 100644
index 0000000..0644ed7
--- /dev/null
+++ b/android_webview/native/aw_contents_lifecycle_notifier.cc
@@ -0,0 +1,27 @@
+// Copyright 2015 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.
+
+#include "android_webview/native/aw_contents_lifecycle_notifier.h"
+
+#include "jni/AwContentsLifecycleNotifier_jni.h"
+
+using base::android::AttachCurrentThread;
+
+namespace android_webview {
+
+bool RegisterAwContentsLifecycleNotifier(JNIEnv* env) {
+  return RegisterNativesImpl(env);
+}
+
+// static
+void AwContentsLifecycleNotifier::OnWebViewCreated() {
+  Java_AwContentsLifecycleNotifier_onWebViewCreated(AttachCurrentThread());
+}
+
+// static
+void AwContentsLifecycleNotifier::OnWebViewDestroyed() {
+  Java_AwContentsLifecycleNotifier_onWebViewDestroyed(AttachCurrentThread());
+}
+
+}  // namespace android_webview
diff --git a/android_webview/native/aw_contents_lifecycle_notifier.h b/android_webview/native/aw_contents_lifecycle_notifier.h
new file mode 100644
index 0000000..7965f11
--- /dev/null
+++ b/android_webview/native/aw_contents_lifecycle_notifier.h
@@ -0,0 +1,26 @@
+// Copyright 2015 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.
+
+#ifndef ANDROID_WEBVIEW_NATIVE_AW_CONTENTS_LIFECYCLE_OBSERVER_H_
+#define ANDROID_WEBVIEW_NATIVE_AW_CONTENTS_LIFECYCLE_OBSERVER_H_
+
+#include "base/android/jni_android.h"
+#include "base/macros.h"
+
+namespace android_webview {
+
+class AwContentsLifecycleNotifier {
+ public:
+  static void OnWebViewCreated();
+  static void OnWebViewDestroyed();
+
+ private:
+  DISALLOW_IMPLICIT_CONSTRUCTORS(AwContentsLifecycleNotifier);
+};
+
+bool RegisterAwContentsLifecycleNotifier(JNIEnv* env);
+
+}  // namespace android_webview
+
+#endif
diff --git a/android_webview/native/webview_native.gyp b/android_webview/native/webview_native.gyp
index 020f0a8..97d941e 100644
--- a/android_webview/native/webview_native.gyp
+++ b/android_webview/native/webview_native.gyp
@@ -50,6 +50,8 @@
         'aw_contents_client_bridge.h',
         'aw_contents_io_thread_client_impl.cc',
         'aw_contents_io_thread_client_impl.h',
+        'aw_contents_lifecycle_notifier.cc',
+        'aw_contents_lifecycle_notifier.h',
         'aw_contents_statics.cc',
         'aw_contents_statics.h',
         'aw_debug.cc',
@@ -135,6 +137,7 @@
           '../java/src/org/chromium/android_webview/AwContentsBackgroundThreadClient.java',
           '../java/src/org/chromium/android_webview/AwContentsClientBridge.java',
           '../java/src/org/chromium/android_webview/AwContentsIoThreadClient.java',
+          '../java/src/org/chromium/android_webview/AwContentsLifecycleNotifier.java',
           '../java/src/org/chromium/android_webview/AwContentsStatics.java',
           '../java/src/org/chromium/android_webview/AwCookieManager.java',
           '../java/src/org/chromium/android_webview/AwDebug.java',