[WebView] Add documentation regarding geolocation api on secure origins.

Update to javadoc comments saying that for apps targeting N and up
the geolocation api is only supported on secure origins.
On non-secure origins requests to geolocation api are automatically
denied without calling the corresponding
WebChromeClient#onGeolocationPermissionsShowPrompt method.

BUG: 28080869
Change-Id: I57726f7f3b3d38db0535f742b1f74c40c1f1ce8b

core/java/android/webkit/WebChromeClient.java

@@ -284,6 +284,13 @@ public class WebChromeClient {
      * currently set for that origin. The host application should invoke the
      * specified callback with the desired permission state. See
      * {@link GeolocationPermissions} for details.
+     *
+     * <p>Note that for applications targeting Android N and later SDKs
+     * (API level > {@link android.os.Build.VERSION_CODES#M})
+     * this method is only called for requests originating from secure
+     * origins such as https. On non-secure origins geolocation requests
+     * are automatically denied.</p>
+     *
      * @param origin The origin of the web content attempting to use the
      *               Geolocation API.
      * @param callback The callback to use to set the permission state for the

core/java/android/webkit/WebView.java

@@ -255,6 +255,16 @@ import java.util.Map;
  * is loading.
  * </p>
  *
+ * <h3>HTML5 Geolocation API support</h3>
+ *
+ * <p>For applications targeting Android N and later releases
+ * (API level > {@link android.os.Build.VERSION_CODES#M}) the geolocation api is only supported on
+ * secure origins such as https. For such applications requests to geolocation api on non-secure
+ * origins are automatically denied without invoking the corresponding
+ * {@link WebChromeClient#onGeolocationPermissionsShowPrompt(String, GeolocationPermissions.Callback)}
+ * method.
+ * </p>
+ *
  * <h3>Layout size</h3>
  * <p>
  * It is recommended to set the WebView layout height to a fixed value or to