Ship Fenix x86_64 builds

[cpeterso]

We need to publish 64-bit builds to the Google Play Store before Google's August 1 deadline requiring 64-bit support (for apps that include native code).

https://android-developers.googleblog.com/2019/01/get-your-apps-ready-for-64-bit.html

It looks like Fenix is only shipping 32-bit ARMv7 and x86 builds:

fenix/.taskcluster.yml

Lines 92 to 93 in 19dd468

	--apk arm/release/app-arm-release-unsigned.apk \
	--apk x86/release/app-x86-release-unsigned.apk \

GeckoView publishes x86_64 builds in Maven, but we haven't actually shipped x86_64 builds to Fennec Nightly users yet. I'm working with Releng and Relman to ship x86_64 Fennec Nightly by the end of this week.

Fenix will need to ship x86_64 builds by Google's August 1 deadline (or take down our 32-bit x86 builds), but I recommend that you wait for Fennec Nightly users to dogfood x86_64 for a couple weeks before shipping x86_64 Fenix builds. The beginning of Fenix M3 (March) would probably be a good time.

(For shipping ARM64 Fenix builds, see issue #444.)

┆Issue is synchronized with this Jira Task

[vesta0]

Will wait a few weeks for Fennec Nightly users to test this. 1.5% of Fennec users have it.

[cpeterso]

@vesta0 and @pocmo - Fennec Nightly has been shipping x86_64 builds since February 13 (Fennec bug 1505538) without any big problems. Thus Fenix and R-B can start shipping x86 and x86_64 builds whenever you like, so I am removing this issue's blocked label.

Admittedly, we don't have many x86 or x86_64 Fennec Nightly users. Based on telemetry, Fennec Nightly's architecture split is:

71.24% ARM64
27.95% ARM 32-bit
 0.76% x86 32-bit
 0.04% x86_64

[cpeterso]

Fenix x86_64 will need support from Application Services:
mozilla/application-services#426

[cpeterso]

Removing Needs GV work label because x86_64 builds of GV already exist. Fennec has been testing x86_64 in Nightly and Beta without any reports of problems (though there are very few x86_64 Fennec users).

https://maven.mozilla.org/?prefix=maven2/org/mozilla/geckoview/geckoview-nightly-x86_64/

[kbrosnan]

This is done.

[cpeterso]

@kbrosnan When were Fenix x86_64 builds first available? I don't see them in the Google Play Store. For yesterday's Fenix and Reference Browser releases (both version 1.0.1918), I see only APKs for armeabi-v7a, arm64-v8a, and x86. Maybe we're building the x86_64 APKs but not uploading them to the Play Store yet?