Define a Java-side global application context.

base/android/java/src/org/chromium/base/ContextUtils.java

+// 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.base;
+
+import android.content.Context;
+
+import org.chromium.base.annotations.CalledByNative;
+import org.chromium.base.annotations.JNINamespace;
+
+/**
+ * This class provides Android Context utility methods.
+ */
+@JNINamespace("base::android")
+public class ContextUtils {
+    private static Context sApplicationContext;
+
+    /**
+     * Get the Android application context.
+     *
+     * Under normal circumstances there is only one application context in a process, so it's safe
+     * to treat this as a global. In WebView it's possible for more than one app using WebView to be
+     * running in a single process, but this mechanism is rarely used and this is not the only
+     * problem in that scenario, so we don't currently forbid using it as a global.
+     *
+     * Do not downcast the context returned by this method to Application (or any subclass). It may
+     * not be an Application object; it may be wrapped in a ContextWrapper. The only assumption you
+     * may make is that it is a Context whose lifetime is the same as the lifetime of the process.
+     */
+    public static Context getApplicationContext() {
+        assert sApplicationContext != null;
+        return sApplicationContext;
+    }
+
+    /**
+     * Initialize the Android application context.
+     *
+     * Either this or the native equivalent base::android::InitApplicationContext must be called
+     * once during startup. JNI bindings must have been initialized, as the context is stored on
+     * both sides.
+     */
+    public static void initApplicationContext(Context appContext) {
+        initJavaSideApplicationContext(appContext);
+        nativeInitNativeSideApplicationContext(appContext);
+    }
+
+    @CalledByNative
+    private static void initJavaSideApplicationContext(Context appContext) {
+        assert appContext != null;
+        assert sApplicationContext == null || sApplicationContext == appContext;
+        sApplicationContext = appContext;
+    }
+
+    private static native void nativeInitNativeSideApplicationContext(Context appContext);
+}