Query sdk-platform-path in build/config/mac/sdk_info.py.

The XCTest support (used for EarlGrey tests) requires linking against
XCTest.framework whose location is relative to sdk-platform-path, so
propagate via ios_sdk_platform_path variable in gn.

BUG=629867

Review-Url: https://codereview.chromium.org/2168873003
Cr-Commit-Position: refs/heads/master@{#407093}

build/config/ios/ios_sdk.gni

@@ -9,6 +9,7 @@ declare_args() {
   ios_sdk_name = ""
   ios_sdk_version = ""
   ios_sdk_platform = ""
+  ios_sdk_platform_path = ""
   xcode_version = ""
   xcode_build = ""
   machine_os_build = ""
@@ -75,6 +76,7 @@ if (ios_sdk_path == "") {
       exec_script("//build/config/mac/sdk_info.py", [ ios_sdk_name ], "scope")
   ios_sdk_path = _ios_sdk_result.sdk_path
   ios_sdk_version = _ios_sdk_result.sdk_version
+  ios_sdk_platform_path = _ios_sdk_result.sdk_platform_path
   ios_sdk_build = _ios_sdk_result.sdk_build
   xcode_version = _ios_sdk_result.xcode_version
   xcode_build = _ios_sdk_result.xcode_build

build/config/mac/sdk_info.py

@@ -39,6 +39,8 @@ def FillSDKPathAndVersion(settings, platform, xcode_version):
       'xcrun', '-sdk', platform, '--show-sdk-path']).strip()
   settings['sdk_version'] = subprocess.check_output([
       'xcrun', '-sdk', platform, '--show-sdk-version']).strip()
+  settings['sdk_platform_path'] = subprocess.check_output([
+      'xcrun', '-sdk', platform, '--show-sdk-platform-path']).strip()
   # TODO: unconditionally use --show-sdk-build-version once Xcode 7.2 or
   # higher is required to build Chrome for iOS or OS X.
   if xcode_version >= '0720':