Add "Available since" text to all android/ headers.

Also fix a few missing/incorrect annotations.

Bug: http://b/143470841
Test: treehugger
Change-Id: I1d9ec8350df03df7d80f1cc2334eef45deec30ec
Merged-In: I1d9ec8350df03df7d80f1cc2334eef45deec30ec
diff --git a/include/android/hardware_buffer_jni.h b/include/android/hardware_buffer_jni.h
index aedf369..293e5ac 100644
--- a/include/android/hardware_buffer_jni.h
+++ b/include/android/hardware_buffer_jni.h
@@ -42,6 +42,8 @@
  * that is returned. To keep the AHardwareBuffer live after the Java
  * HardwareBuffer object got garbage collected, be sure to use AHardwareBuffer_acquire()
  * to acquire an additional reference.
+ *
+ * Available since API level 26.
  */
 AHardwareBuffer* AHardwareBuffer_fromHardwareBuffer(JNIEnv* env,
         jobject hardwareBufferObj) __INTRODUCED_IN(26);
@@ -49,6 +51,8 @@
 /**
  * Return a new Java HardwareBuffer object that wraps the passed native
  * AHardwareBuffer object.
+ *
+ * Available since API level 26.
  */
 jobject AHardwareBuffer_toHardwareBuffer(JNIEnv* env,
         AHardwareBuffer* hardwareBuffer) __INTRODUCED_IN(26);