Adding GetCurrentThreadPriority API in Android platform.

This change takes care of implementing GetCurrentThreadPriory in
Android platform. Currently it is left NOTIMPLEMENTED(), due to
which some unit test cases has to mark not to execute on Android.

BUG=505474

Review URL: https://codereview.chromium.org/1216933009

Cr-Commit-Position: refs/heads/master@{#351563}

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

@@ -210,4 +210,14 @@ public static Looper getUiThreadLooper() {
     public static void setThreadPriorityAudio(int tid) {
         Process.setThreadPriority(tid, Process.THREAD_PRIORITY_AUDIO);
     }
+
+    /**
+     * Checks whether Thread priority is THREAD_PRIORITY_AUDIO or not.
+     * @param tid Thread id.
+     * @return true for THREAD_PRIORITY_AUDIO and false otherwise.
+     */
+    @CalledByNative
+    private static boolean isThreadPriorityAudio(int tid) {
+        return Process.getThreadPriority(tid) == Process.THREAD_PRIORITY_AUDIO;
+    }
 }

base/threading/platform_thread_android.cc

@@ -49,8 +49,14 @@ bool SetCurrentThreadPriorityForPlatform(ThreadPriority priority) {
 }
 
 bool GetCurrentThreadPriorityForPlatform(ThreadPriority* priority) {
-  // See http://crbug.com/505474.
-  NOTIMPLEMENTED();
+  DCHECK(priority);
+  *priority = ThreadPriority::NORMAL;
+  JNIEnv* env = base::android::AttachCurrentThread();
+  if (Java_ThreadUtils_isThreadPriorityAudio(
+      env, PlatformThread::CurrentId())) {
+    *priority = ThreadPriority::REALTIME_AUDIO;
+    return true;
+  }
   return false;
 }