Implements JavaToNativeStringMap and adds tests for native API.

Implements JavaToNativeStringMap that is a replacement for
JavaToStdMapStrings. It uses a new template method JavaToNativeMap. Also
adds testing support for native API and a test for JavaToNativeStringMap.

Bug: webrtc:8769
Change-Id: I580d4992a899ebe02da39af450fa51d52ee9b88b
Reviewed-on: https://webrtc-review.googlesource.com/48060
Reviewed-by: Magnus Jedvert <magjed@webrtc.org>
Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
Commit-Queue: Sami Kalliomäki <sakal@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#21967}

sdk/android/native_unittests/java_types_unittest.cc

@@ -0,0 +1,35 @@
+/*
+ *  Copyright (c) 2018 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include <memory>
+#include <vector>
+
+#include "sdk/android/generated_native_unittests_jni/jni/JavaTypesTestHelper_jni.h"
+#include "sdk/android/native_api/jni/java_types.h"
+#include "test/gtest.h"
+
+namespace webrtc {
+namespace test {
+namespace {
+TEST(JavaTypesTest, TestJavaToNativeStringMap) {
+  JNIEnv* env = AttachCurrentThreadIfNeeded();
+  ScopedJavaLocalRef<jobject> j_map =
+      Java_JavaTypesTestHelper_createTestStringMap(env);
+
+  std::map<std::string, std::string> output = JavaToNativeStringMap(env, j_map);
+
+  std::map<std::string, std::string> expected{
+      {"one", "1"}, {"two", "2"}, {"three", "3"},
+  };
+  EXPECT_EQ(expected, output);
+}
+}  // namespace
+}  // namespace test
+}  // namespace webrtc

sdk/android/native_unittests/org/webrtc/JavaTypesTestHelper.java

@@ -0,0 +1,25 @@
+/*
+ *  Copyright (c) 2018 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+package org.webrtc;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class JavaTypesTestHelper {
+  @CalledByNative
+  public static Map createTestStringMap() {
+    Map<String, String> testMap = new HashMap<String, String>();
+    testMap.put("one", "1");
+    testMap.put("two", "2");
+    testMap.put("three", "3");
+    return testMap;
+  }
+}

sdk/android/native_unittests/test_jni_onload.cc

@@ -0,0 +1,23 @@
+/*
+ *  Copyright (c) 2018 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include <jni.h>
+#undef JNIEXPORT
+#define JNIEXPORT __attribute__((visibility("default")))
+
+#include "rtc_base/checks.h"
+#include "sdk/android/native_api/base/init.h"
+#include "sdk/android/native_api/jni/java_types.h"
+
+// This is called by the VM when the shared library is first loaded.
+JNIEXPORT jint JNI_OnLoad(JavaVM* vm, void* reserved) {
+  webrtc::InitAndroid(vm);
+  return JNI_VERSION_1_4;
+}