[Mono.Android] abstract-ify inconsistent android.webkit API.

[atsushieno]

As part of discussion at #1078 (comment) ,
we decided to make changes to those inconsistent methods that used to be
virtual and then became abstract, to become abstract even in old API level.

It is done at metadata fixup level.

[atsushieno]

This needs changes in xamarin-android-api-compatibility too.

[atsushieno]

build

[jonpryor]

#1303 (comment)

[jonpryor]

I think these changes are too aggressive. The listed changes:

<h2>Namespace Android.Webkit</h2>
<!-- start type WebHistoryItem --> <div>
<h3>Type Changed: Android.Webkit.WebHistoryItem</h3>
<p>Modified properties:</p>
<pre>
<div data-is-breaking>	public <span class='added added-breaking-inline'>abstract</span> int Id { get; }
</div></pre>

This turns WebHistoryItem.getId() into an abstract member. However:

1. WebHistoryItem no longer documents any getId() method, and
2. The last API level to declare a WebHistoryItem.getId() method -- API-16 -- didn't declare it as abstract either.

So why was this method changed at all?

<h3>Type Changed: Android.Webkit.WebSettings</h3>
<p>Modified properties:</p>
<pre>
<div data-is-breaking>	public <span class='added added-breaking-inline'>abstract</span> bool NavDump { get; set; }
</div><div data-is-breaking>	public <span class='added added-breaking-inline'>abstract</span> bool PluginsEnabled { get; set; }
</div><div data-is-breaking>	public <span class='added added-breaking-inline'>abstract</span> string PluginsPath { get; set; }
</div><div data-is-breaking>	public <span class='added added-breaking-inline'>abstract</span> bool UseDoubleTree { get; set; }
</div><div data-is-breaking>	public <span class='added added-breaking-inline'>abstract</span> bool UseWebViewBackgroundForOverscrollBackground { get; set; }
</div><div data-is-breaking>	public <span class='added added-breaking-inline'>abstract</span> int UserAgent { get; set; }
</div></pre>
<p>Modified methods:</p>
<pre>
<div data-is-breaking>	public <span class='added added-breaking-inline'>abstract</span> WebSettings.TextSize GetTextSize ()
</div></pre>

These changes are in the same boat: WebSettings does not declare any of the methods getNavDump(), getPluginsEnabled(), getPluginsPath(), getUseDoubleTree(), getUseWebViewBackgroundForOverscrollBackground(), or getUserAgent(). These were apparently removed in API-17

In API-16 -- the last API level they appeared in -- none of those methods are abstract.

Thus, why are we turning these deprecated and no longer public members into abstract members?

[jonpryor]

Regarding our previous discussion:

I'd suggest to change those "virtual in the past, now abstract" members to abstract AT ALL, using metadata fixup

My interpretation of this was that if a member was virtual in API-X, and became abstract in API-(X+1), then we should change this member to be abstract in all API levels.

I agree with my interpretation. For example, consider CookieManager.hasCookies(): this was non-abstract in API-1, and became abstract in API-22. By this logic, we should make the CookieManager.HasCookies property abstract in all API levels, and I'd agree with that.

This PR does not fit the above description, not in my mind. This PR is turning methods which were always non-abstract members into abstract members -- a sure fire API break, as nobody will have ever overridden these members before! -- and, as a double whammy, is turning methods which no longer exist into abstract methods.

As such, this PR would make our binding worse: anybody deriving from WebSettings will need to override and implement more members than a Java developer would need to do.

[atsushieno]

huh, I am confused. With the latest run-api-compatibility-tests they are indeed not reported as inter-api breakage anymore. Then there is no reason to make API changes (I don't want to dare to deal with it either).

[jonpryor]

The probable reason that run-api-compatibility-tests doesn't flag them as problematic is because it uses mono-api-html --ignore-changes-virtual, which ignores changes from virtual to abstract.