[iOS] Fix compilation of official build with Xcode 8.

build/config/mac/mac_sdk.gni

Index: build/config/mac/mac_sdk.gni
diff --git a/build/config/mac/mac_sdk.gni b/build/config/mac/mac_sdk.gni
index eb0fdda61492d095fc13f6586316e4b11162610f..2d3b4af19e115a2936232c46d8b46d470325704d 100644
--- a/build/config/mac/mac_sdk.gni
+++ b/build/config/mac/mac_sdk.gni
@@ -25,8 +25,11 @@ declare_args() {
   mac_sdk_name = "macosx"
 }
 
+_verify_sdk = is_chrome_branded && is_official_build &&
+              current_toolchain != host_toolchain

[Dirk Pranke, 2016/08/08 23:15:06]

I know we discussed this a bit back and forth over email, but I think you maybe
drew the wrong conclusion, and I think it's fine to require the same sdk version
for both target and host toolchains.

It is reasonable to still guard this on something since we don't need to call
things twice, though.

[sdefresne, 2016/08/08 23:21:27]

The issue is that Chrome on iOS wants to soon require Xcode 8 for the
compilation. One of the bots we have sets both is_chrome_branded and
is_official_build to true (it is used to build the version that is tested).

The problem is that those flags are propagated from the main toolchain to the
host toolchain. When building the tools for the host toolchain, we do not really
care about building and official / branded version, we're fine with just
building release.

Since Xcode 8 does not contains 10.10 SDK, the "gn gen" steps fails with the
following error:

  ERROR at //build/config/mac/mac_sdk.gni:43:34: Array subscript out of range.
  mac_sdk_version = find_sdk_lines[1]
                                   ^
  You gave me 1 but I was expecting something from 0 to 1, inclusive.

(issue https://codereview.chromium.org/2218773004/ is here to make the error
cleaner).

Maybe the correct check should be target_os != "ios" instead. WDYT?

[Dirk Pranke, 2016/08/08 23:36:28]

Change to current_toolchain == default_toolchain, maybe (as we discussed).

+
 find_sdk_args = [ "--print_sdk_path" ]
-if (is_chrome_branded && is_official_build) {
+if (_verify_sdk) {
   find_sdk_args += [
     "--verify",
     mac_sdk_min,