Remove Xamarin.Android.Support.v7.MediaRouter

[jonathanpeppers]

Description of Change

Context: dotnet/android#2982

The Blank Xamarin.Forms app template in VS 2019 takes longer to build
than in VS 2017. A little research is showing that this is due to use
of the 28.x support libraries... For example, the build includes ~20
more jar files in the template from 2019 than 2017. The
_CompileDex step alone goes from ~15.2s to ~18.2s.

This lead me down the road of investigating if we can remove any
support libraries by default in Xamarin.Forms apps. I am also seeing
if there is more we can do in Xamarin.Android for this problem, in
general.

It looks like we can remove:

• Xamarin.Android.Support.v7.MediaRouter
• Xamarin.Android.Support.Media.Compat

Neither of these appear to be used, but have been listed as
dependencies of Xamarin.Forms for a long time.

Results

I made these changes, then did a Debug build of
Xamarin.Forms.ControlGallery.Android.csproj for comparison.

Comparing dex file sizes (in bytes):

Before:
3428092 classes.dex
3265616 classes2.dex
6693708 total
After:
4938000 classes.dex
1098772 classes2.dex
6036772 total

This looks like it could potentially save ~600KB of compiled dex code
on every Xamarin.Forms app.

Comparing methods:

Before:
classes.dex  11,492 methods
classes2.dex 19,451 methods
total        30,943 methods
After:
classes.dex  22,171 methods
classes2.dex  7,635 methods
total        29,806 methods

~1,137 methods removed, which should help with the dex limit.

Comparing APK sizes (in bytes):

Before:
26442597 AndroidControlGallery.AndroidControlGallery-Signed.apk
After:
25741701 AndroidControlGallery.AndroidControlGallery-Signed.apk

~700KB smaller APK, due to less .NET assemblies & dex code.

Comparing build time (this was using dx):

Before:
19785 ms  CompileToDalvik                            1 calls
After:
18532 ms  CompileToDalvik                            1 calls

Looks like it saved over a second of build time for this project.

Seems like an "easy win", let's do this!

Issues Resolved

none

API Changes

None

Platforms Affected

• Android

Behavioral/Visual Changes

Only known behavior, is a user might have to add <PackageReference Include="Xamarin.Android.Support.v7.MediaRouter" Version="28.0.0.1" /> if they are using it directly.

Before/After Screenshots

Not applicable

Testing Procedure

If Xamarin.Forms apps build with this change, things should work.

PR Checklist

• Has automated tests
• Rebased on top of the target branch at time of PR
• Changes adhere to coding standard

[rmarinho]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[jonathanpeppers]

I'm not sure how to read these CI results?

I mostly see things like this:

Access denied. public Build Service (xamarin) needs Edit build quality permissions for vstfs:///Build/Build/1115 in team project public to perform the action.

If there is a failure here, ping me and I'll take a look. Thanks!

[PureWeen]

UI Tests seem fine

Once @paymicro approves we can merge