commit ae5fd322fd40d5a4cfd6ae4bc6bb828b189512ac
author Nate Fischer <ntfschr@chromium.org> Fri Jan 11 07:33:18 2019
committer Commit Bot <commit-bot@chromium.org> Fri Jan 11 07:33:18 2019
tree 3e035fa0469f0f7c5c37eb2a267f87ca6a0db99e
parent 3270b139a830b6f1082923855a6b6a9d4af4b923

Docs: document target_cpu in Android steps

This updates Android build documentation for the `target_cpu` option,
and provides guidance for how to determine this value.

This setting is arm-by-default for Android development. Although this is
OK for Chrome for Android developers, it doesn't work for several
use-cases:

 * Doesn't work for WebView on arm64 devices (which are increasingly
   popular)
 * Doesn't work for tests on arm64 devices (e.g.,
   webview_instrumentation_apk)
 * Doesn't work for non-arm at all (e.g., x86-based emulator)

Although there's a low cost to setting `target_cpu`, there's a high cost
to omitting it (a mistake requires a full rebuild). And, since it's not
obvious when the default is insufficient, this provides guidance for how
to set it correctly for a given device.

This also changes from `gn gen --args` to `gn args`. The motivation is:

 * It's convenient to call out `target_cpu` with an inline comment
 * `gn args` is a convenient command for complex configs, and isn't
   significantly worse for the recommended simple config
 * IMO it's easier to find docs for `gn args` (`gn help args`) than
   `--args` (it's not obvious it's a global option, and lives under `gn
   help switches`)

This edits a bullet about default settings. Although it's true that
`target_os` and `target_cpu` default to `host_os` and `host_cpu`, this
is not relevant to Android development, since we always override these
values.

R=agrieve@chromium.org

Bug: 918221
Test: N/A
Change-Id: Ie4b8eab491fd8b860420dbba6dac6badc16b9f76
Reviewed-on: https://chromium-review.googlesource.com/c/1401981
Commit-Queue: Nate Fischer <ntfschr@chromium.org>
Reviewed-by: agrieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/master@{#621936}