While we wait for bots to be updated with jdk8 (#662467), we should implement this by:
1. Adding retrolambda to third_party (https://www.chromium.org/developers/adding-3rd-party-libraries)
2. Hook it into the process_prebuilt step (for targets where supports_android_true) behind a GN flag: use_java8. This should also set the --java-version when invoking javac.py to be "1.8" (when use_java8, but irrespective of supports_android).

The following revision refers to this bug:
  https://chrome-internal.googlesource.com/clank/internal/apps/+/de448835eca85cbada700ba028af6c6a70c84436

commit de448835eca85cbada700ba028af6c6a70c84436
Author: F <zpeng@google.com>
Date: Tue Nov 29 19:16:00 2016

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d8c7a8acef06acc9f093177d568789f8f3329c23

commit d8c7a8acef06acc9f093177d568789f8f3329c23
Author: zpeng <zpeng@chromium.org>
Date: Thu Dec 01 16:56:51 2016

Adds experimental support for Java 8 via gn arg

Requires host machines to have jdk8 installed and uses retrolambda to
convert java 8 .jar files into java 7 .jar files.

Future work includes adding Retrolambda into third_party libraries.

BUG= 642600 

Review-Url: https://codereview.chromium.org/2543463002
Cr-Commit-Position: refs/heads/master@{#435629}

[modify] https://crrev.com/d8c7a8acef06acc9f093177d568789f8f3329c23/build/android/gyp/javac.py
[add] https://crrev.com/d8c7a8acef06acc9f093177d568789f8f3329c23/build/android/gyp/retrolambda.py
[modify] https://crrev.com/d8c7a8acef06acc9f093177d568789f8f3329c23/build/config/android/config.gni
[modify] https://crrev.com/d8c7a8acef06acc9f093177d568789f8f3329c23/build/config/android/internal_rules.gni
[modify] https://crrev.com/d8c7a8acef06acc9f093177d568789f8f3329c23/build/config/android/rules.gni

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/3353ce430e3f6f1eaa5e16b998d66a5fc915b736

commit 3353ce430e3f6f1eaa5e16b998d66a5fc915b736
Author: zpeng <zpeng@chromium.org>
Date: Wed Dec 07 16:06:02 2016

Checking in retrolambda into third_party/

Retrolambda will be used to transform Java 8's bytecode to Java 7's
bytecode so that Java 8 features such as lamba expressions can be used
on Chrome for Android without switching from javac to Jack.

BUG= 642600 

Review-Url: https://codereview.chromium.org/2559553002
Cr-Commit-Position: refs/heads/master@{#436968}

[modify] https://crrev.com/3353ce430e3f6f1eaa5e16b998d66a5fc915b736/.gitignore
[modify] https://crrev.com/3353ce430e3f6f1eaa5e16b998d66a5fc915b736/DEPS
[add] https://crrev.com/3353ce430e3f6f1eaa5e16b998d66a5fc915b736/third_party/retrolambda/LICENSE.txt
[add] https://crrev.com/3353ce430e3f6f1eaa5e16b998d66a5fc915b736/third_party/retrolambda/OWNERS
[add] https://crrev.com/3353ce430e3f6f1eaa5e16b998d66a5fc915b736/third_party/retrolambda/README.chromium
[add] https://crrev.com/3353ce430e3f6f1eaa5e16b998d66a5fc915b736/third_party/retrolambda/retrolambda-2.3.0.jar.sha1

Here is a reference CL that uses lambdas:
https://codereview.chromium.org/2759963002

It currently fails on checkstyle and android lint (the two blocked-on bugs).

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b5d37e705dd1caea0446240e7381d28470d33218

commit b5d37e705dd1caea0446240e7381d28470d33218
Author: zpeng <zpeng@chromium.org>
Date: Wed May 03 18:56:18 2017

Update retrolambda to 2.5.1

BUG= 642600 

Review-Url: https://codereview.chromium.org/2854323004
Cr-Commit-Position: refs/heads/master@{#469056}

[modify] https://crrev.com/b5d37e705dd1caea0446240e7381d28470d33218/build/android/gyp/retrolambda.py
[modify] https://crrev.com/b5d37e705dd1caea0446240e7381d28470d33218/third_party/retrolambda/README.chromium
[delete] https://crrev.com/9b15a04b5406ec7b03a525aed953c804ff15813e/third_party/retrolambda/retrolambda-2.3.0.jar.sha1
[add] https://crrev.com/b5d37e705dd1caea0446240e7381d28470d33218/third_party/retrolambda/retrolambda-2.5.1.jar.sha1

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f0f89654334792a032ac1f49c3e988f4b87cf2ed

commit f0f89654334792a032ac1f49c3e988f4b87cf2ed
Author: zpeng <zpeng@chromium.org>
Date: Wed May 10 19:43:54 2017

Run lint on javac output instead of process_java_prebuilt output.

During the process_java_prebuilt step, javac output might be modified
by retrolambda. As a result, if lint is run on processed_java_prebuilt
output, lint might not give the correct results. This CL makes lint run
on javac output instead of process_java_prebuilt output to eliminate
this possibility.

BUG= 642600 

Review-Url: https://codereview.chromium.org/2871283002
Cr-Commit-Position: refs/heads/master@{#470673}

[modify] https://crrev.com/f0f89654334792a032ac1f49c3e988f4b87cf2ed/build/config/android/internal_rules.gni

Merging into the "use desugar" bug.