[android_webview] Introduce AwAssets to reference assets inside the apk.

android_webview/native/aw_assets.h

Index: android_webview/native/aw_assets.h
diff --git a/android_webview/native/aw_assets.h b/android_webview/native/aw_assets.h
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+++ b/android_webview/native/aw_assets.h
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+// Copyright 2014 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_ASSETS_H_
+#define ANDROID_WEBVIEW_NATIVE_AW_ASSETS_H_
+
+#include <string>
+
+#include "base/android/jni_android.h"
+
+namespace android_webview {
+namespace AwAssets {
+
+// Called by native to retrieve an asset (e.g. a .pak file) from the apk.
+// Returns: true in case of success, false otherwise.
+// Output arguments:
+// - |fd|: file descriptor to the apk. The caller takes the ownership.
+// - |offset|: offset in bytes from the start of the file
+// - |size|: size in bytes of the asset / resource.
+bool OpenAsset(const std::string& filename,
+               int* fd,
+               int64* offset,
+               int64* size);
+
+}  // namespace AwAssets
+
+bool RegisterAwAssets(JNIEnv* env);
+
+}  // namsespace android_webview
+
+#endif  // ANDROID_WEBVIEW_NATIVE_AW_ASSETS_H_