android: Introduce a ui::PlatformWindow implementation for android.

ui/platform_window/android/BUILD.gn

+# 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.
+
+import("//build/config/android/rules.gni")
+import("//testing/test.gni")
+
+assert(is_android)
+
+component("android") {
+  output_name = "android_window"
+  sources = [
+    "platform_window_android.cc",
+    "platform_window_android.h",
+  ]
+
+  defines = [ "ANDROID_WINDOW_IMPLEMENTATION" ]
+
+  deps = [
+    "//base",
+    "//skia",
+    "//ui/events:events_base",
+    "//ui/gfx",
+    "//ui/gfx/geometry",
+    ":jni_headers",
+    ":platform_window_java",
+  ]
+}
+
+generate_jni("jni_headers") {
+  sources = [
+    "java/src/org/chromium/ui/PlatformWindowAndroid.java",
+  ]
+  jni_package = "android_window"
+}
+
+android_library("platform_window_java") {
+  java_files = [ "java/src/org/chromium/ui/PlatformWindowAndroid.java" ]
+  deps = [
+    "//base:base_java",
+  ]
+}