[Android] Trigger native event batching through Feature API

content/public/android/java/src/org/chromium/content/browser/ContentFeatureList.java

Index: content/public/android/java/src/org/chromium/content/browser/ContentFeatureList.java
diff --git a/content/public/android/java/src/org/chromium/content/browser/ContentFeatureList.java b/content/public/android/java/src/org/chromium/content/browser/ContentFeatureList.java
new file mode 100644
index 0000000000000000000000000000000000000000..5312887f53393f486d8d1e0d7c91ee8494ced036
--- /dev/null
+++ b/content/public/android/java/src/org/chromium/content/browser/ContentFeatureList.java
@@ -0,0 +1,36 @@
+// Copyright 2017 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.
+
+package org.chromium.content.browser;
+
+import org.chromium.base.annotations.JNINamespace;
+import org.chromium.base.annotations.MainDex;
+
+/**
+ * Java accessor for base/feature_list.h state.
+ */
+@JNINamespace("content::android")
+@MainDex
+public abstract class ContentFeatureList {

[Ilya Sherman, 2017/03/16 03:39:49]

Hmm, I think it would be nice to provide a more full implementation, to match
what ChromeFeatureList offers.  I'd definitely encourage you to write tests for
your feature, which means you'll likely want a way to explicitly enable or
disable the feature for tests.

But, I'm realizing now that the ChromeFeatureList implementation is all static
methods... I'm not sure what a good way to share the implementation details
would be.  Something something generics?  Please check with someone who's more
familiar with Java best-practices as to what they'd recommend.

[chongz, 2017/03/16 16:12:21]

My feature is about Android native event batching, and I'm not sure if there is
a way to simulate it other than checking if the flag was set...

Also I'm not sure about Android best-practices - I thought I should only add
APIs when I need them, no?
agrieve@ Can I have some suggestions on the recommended pattern? Thanks!

FYI: There seems to be efforts on moving the implementation into //base but
failed due to access issue.
https://codereview.chromium.org/1538573004/diff/180001/chrome/android/java/sr...

[Ilya Sherman, 2017/03/16 17:38:53]

Hmm, it's not very clear to me exactly what you mean.  Could you please point me
to the code that tests the feature?  In particular, there is probably some code
that calls into your feature -- do you do anything to test that that call works
correctly?
I agree that if we're going to be more or less copy/pasting the implementation,
then it's not appropriate to add more features at this time.  I'm just hoping
that we can somehow share the implementations.

[chongz, 2017/03/16 18:54:04]

Sure. Basically everything about this feature is "Call
|View.requestUnbufferedDispatch()| => Android will dispatch events to Clank at a
higher frequency".
There is no tests and I can't think of a way to check if Android handles
|View.requestUnbufferedDispatch()| correctly or simulate an user scroll and see
if we indeed receive events at a higher frequency...
See:
https://codereview.chromium.org/2710683003/diff/40001/content/public/android/...


Or are you suggesting that I should check if the feature flag was passed in and
successfully received?
I'm guessing it means we can keep things as it is until a better solution was
found? 

[Ilya Sherman, 2017/03/16 18:59:12]

Ah, I think I see what you're saying now.  Okay, I suppose that makes sense. 
Thanks for the explanation!
Yep, sounds reasonable for now.

+    // Prevent instantiation.
+    private ContentFeatureList() {}
+
+    /**
+     * Returns whether the specified feature is enabled or not.
+     *
+     * Note: Features queried through this API must be added to the array
+     * |kFeaturesExposedToJava| in content/browser/android/content_feature_list.cc
+     *
+     * @param featureName The name of the feature to query.
+     * @return Whether the feature is enabled or not.
+     */
+    public static boolean isEnabled(String featureName) {
+        return nativeIsEnabled(featureName);
+    }
+
+    // Alphabetical:
+    public static final String REQUEST_UNBUFFERED_DISPATCH = "RequestUnbufferedDispatch";
+
+    private static native boolean nativeIsEnabled(String featureName);
+}