Replace use of --board with --boards in Simple Chrome gclient hook.

This will let folks check out multiple board SDKs at once without
having to modify their .gclient file each time.

Needs to land after crrev.com/c/2163589.

Bug: 937821
Change-Id: I191985b4d5044c84009b8a7d05e33785b6e81e37
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2163849Reviewed-by: Takuto Ikuta <tikuta@chromium.org>
Reviewed-by: Erik Chen <erikchen@chromium.org>
Commit-Queue: Ben Pastene <bpastene@chromium.org>
Cr-Commit-Position: refs/heads/master@{#763367}

DEPS

@@ -143,12 +143,12 @@ vars = {
 
   # Default to the empty board. Desktop Chrome OS builds don't need cros SDK
   # dependencies. Other Chrome OS builds should always define this explicitly.
-  'cros_board': '',
+  'cros_boards': '',
   # Building for CrOS is only supported on linux currently.
-  'checkout_simplechrome': '(checkout_chromeos and host_os == "linux") and ("{cros_board}" != "")',
+  'checkout_simplechrome': '(checkout_chromeos and host_os == "linux") and ("{cros_boards}" != "")',
   # Surround the board var in quotes so gclient doesn't try parsing the string
   # as an expression.
-  'cros_download_vm': '(("{cros_board}" == "amd64-generic") or ("{cros_board}" == "betty")) or ("{cros_board}" == "betty-pi-arc")',
+  'cros_download_vm': '(("{cros_boards}" == "amd64-generic") or ("{cros_boards}" == "betty")) or ("{cros_boards}" == "betty-pi-arc")',
   # Should we build and test for public (ie: full) CrOS images, or private
   # (ie: release) images.
   'use_public_cros_config': 'not checkout_src_internal',
@@ -4337,7 +4337,7 @@ hooks = [
       '--fallback-versions=10',
       '--nogn-gen',
       '--download-vm',
-      '--board={cros_board}',
+      '--boards={cros_boards}',
       '--cache-dir=src/build/cros_cache/',
       # TODO(crbug.com/834134): Remove the cache clobber when the sdk is smart
       # enough to eject old toolchains from the cache.
@@ -4357,7 +4357,7 @@ hooks = [
       '--use-external-config',
       '--fallback-versions=10',
       '--nogn-gen',
-      '--board={cros_board}',
+      '--boards={cros_boards}',
       '--cache-dir=src/build/cros_cache/',
       '--log-level=error',
       '--no-shell',

build/args/chromeos/README.md

@@ -4,7 +4,8 @@ Files in this directory are populated by running `gclient sync` with specific
 arguments set in the .gclient file. Specifically:
 * The file must have a top-level variable set: `target_os = ["chromeos"]`
 * The `"custom_vars"` parameter of the chromium/src.git solution must include the
-  parameter: `"cros_board": "{BOARD_NAME}"`
+  parameter: `"cros_boards": "{BOARD_NAMES}"` where `{BOARD_NAMES}` is a
+  colon-separated list of boards you'd like to checkout.
 
 A typical .gclient file is a sibling of the src/ directory, and might look like
 this:
@@ -17,7 +18,7 @@ solutions = [
     "custom_deps": {},
     "custom_vars" : {
         "checkout_src_internal": True,
-        "cros_board": "eve",
+        "cros_boards": "eve",
     },
   },
 ]
@@ -41,5 +42,5 @@ use_goma = true
 goma_dir = "/path/to/goma/"
 ```
 
-TODO(bpastene): Add list support to gclient and allow multiple boards to be
-specified in the .gclient file.
+TODO(bpastene): Make 'cros_boards' a first class citizen in gclient and replace
+it with 'target_boards' instead.