The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/69fa141b674b850d51439434c4e57081993a44a4

commit 69fa141b674b850d51439434c4e57081993a44a4
Author: Peter Wen <wnwen@chromium.org>
Date: Mon May 14 14:50:19 2018

Android: Add ndk path for generate_gradle.py

This way Android Studio makes use of our existing android ndk rather
than having to download a whole new ndk in third_party/android_tools.

Bug:  840542 
Change-Id: Idcf06675f5e5f74cd860570102c38ae20dd97807
Reviewed-on: https://chromium-review.googlesource.com/1054439
Reviewed-by: agrieve <agrieve@chromium.org>
Reviewed-by: Eric Stevenson <estevenson@chromium.org>
Commit-Queue: Peter Wen <wnwen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#558305}
[modify] https://crrev.com/69fa141b674b850d51439434c4e57081993a44a4/build/android/BUILD.gn
[modify] https://crrev.com/69fa141b674b850d51439434c4e57081993a44a4/build/android/gradle/generate_gradle.py

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/cb5195733a446c14b1c55670c73509fe8b9f9346

commit cb5195733a446c14b1c55670c73509fe8b9f9346
Author: Peter Wen <wnwen@chromium.org>
Date: Wed May 16 17:39:18 2018

Android: Use default sdk dir for Android Studio

Rather than use `third_party/android_tools/sdk` and
`third_party/android_ndk`, create and use the default `~/Android/Sdk`
directory instead for Android Studio. This allows a consistent dev
environment that does not change per-repository and also allows frequent
updates without affecting each checkout.

Necessary for native support and emulators. This will become the default
in the near future. For now, use:

build/android/gradle/generate_gradle.py --sdk AndroidStudioDefault

Bug:  840542 ,620034
Change-Id: Ia482cb2982472410fe9c515c5f5f9856f3eadfaf
Reviewed-on: https://chromium-review.googlesource.com/1058308
Commit-Queue: Peter Wen <wnwen@chromium.org>
Reviewed-by: agrieve <agrieve@chromium.org>
Reviewed-by: Eric Stevenson <estevenson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#559166}
[modify] https://crrev.com/cb5195733a446c14b1c55670c73509fe8b9f9346/build/android/gradle/generate_gradle.py
[modify] https://crrev.com/cb5195733a446c14b1c55670c73509fe8b9f9346/docs/android_studio.md

Each dev with --sdk AndroidStudioDefault can now download ndk and cmake once and not have to download it again. Thus we don't need to include them in our repository.