Revert "Update Android NDK to r16"

This reverts commit 2c1e00697d3c3d087f4d84eaf2c4c40a3e7a0530.

Reason for revert: Breaks MIPS and x86/x64 builders.

Original change's description:
> Update Android NDK to r16
> 
> This contains all the src/ changes necessary to make
> Chromium compile with Android NDK r16. Most changes
> are to make the code compatible with the unified
> headers that are used now.
> 
> The libwebm revision is updated to a newer version in
> order to get a fix for using unified headers that was
> added a while back, but never rolled into Chromium.
> 
> Sister CLs:
> src/third_party/skia/: https://skia-review.googlesource.com/c/skia/+/75422
> src/third_party/android_tools/ndk/: https://chromium-review.googlesource.com/c/android_ndk/+/784230
> 
> Bug: 771171
> Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
> Change-Id: I643f9f7bd75d111e540778d2fdf8c20851485a5a
> Reviewed-on: https://chromium-review.googlesource.com/777822
> Commit-Queue: Brian Sheedy <[email protected]>
> Reviewed-by: Robert Sesek <[email protected]>
> Reviewed-by: Ross McIlroy <[email protected]>
> Reviewed-by: Tom Sepez <[email protected]>
> Reviewed-by: Pavel Feldman <[email protected]>
> Reviewed-by: Scott Graham <[email protected]>
> Reviewed-by: Zhongyi Shi <[email protected]>
> Reviewed-by: Daniel Cheng <[email protected]>
> Reviewed-by: Ryan Sturm <[email protected]>
> Reviewed-by: Dale Curtis <[email protected]>
> Reviewed-by: agrieve <[email protected]>
> Cr-Commit-Position: refs/heads/master@{#525076}

[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected]

Change-Id: Ie24d902f9fa6f7c8add5ba553405dcfe6e8e4f5a
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 771171
Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Reviewed-on: https://chromium-review.googlesource.com/834608
Reviewed-by: Brian Sheedy <[email protected]>
Commit-Queue: Brian Sheedy <[email protected]>
Cr-Commit-Position: refs/heads/master@{#525096}
31 files changed