Make mac target compile inside ios build also use xcode in src.

Since it is out of src by default, it is not possible for us to provide
hermetic compile.  Let me make that within Chromium src.

Bug: 1015730
Change-Id: I4283a6ccf54d8f30401a6ad3f0084b7fe791b2be
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2027015
Auto-Submit: Yoshisato Yanagisawa <yyanagisawa@chromium.org>
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Commit-Queue: Yoshisato Yanagisawa <yyanagisawa@chromium.org>
Cr-Commit-Position: refs/heads/master@{#738460}

build/config/mac/mac_sdk.gni

@@ -4,6 +4,7 @@
 
 import("//build/config/chrome_build.gni")
 import("//build/config/mac/mac_sdk_overrides.gni")
+import("//build/toolchain/goma.gni")
 import("//build/toolchain/toolchain.gni")
 
 declare_args() {
@@ -79,22 +80,6 @@ if (_verify_sdk) {
   find_sdk_args += [ mac_sdk_min ]
 }
 
-# The tool will print the SDK path on the first line, and the version on the
-# second line.
-find_sdk_lines =
-    exec_script("//build/mac/find_sdk.py", find_sdk_args, "list lines")
-mac_sdk_version = find_sdk_lines[2]
-if (mac_sdk_path == "") {
-  mac_sdk_path = find_sdk_lines[0]
-}
-mac_bin_path = find_sdk_lines[1]
-
-# If we're using hermetic Xcode, then we want the paths to be relative so that
-# generated ninja files are independent of the directory location.
-if (!use_system_xcode) {
-  mac_bin_path = rebase_path(mac_bin_path, root_build_dir)
-}
-
 script_name = "//build/config/mac/sdk_info.py"
 sdk_info_args = []
 if (!use_system_xcode) {
@@ -103,12 +88,41 @@ if (!use_system_xcode) {
     _hermetic_xcode_path,
   ]
 }
+
+# put system xcode under src to avoid absolute path.
+if (use_system_xcode && ios_use_goma_rbe) {
+  sdk_info_args += [
+    "--create_symlink_under_src",
+    "--get_sdk_info",
+  ]
+}
 sdk_info_args += [ mac_sdk_name ]
 
 _mac_sdk_result = exec_script(script_name, sdk_info_args, "scope")
 xcode_version = _mac_sdk_result.xcode_version
 xcode_build = _mac_sdk_result.xcode_build
 machine_os_build = _mac_sdk_result.machine_os_build
+if (mac_sdk_path == "" && use_system_xcode && ios_use_goma_rbe) {
+  mac_sdk_path = _mac_sdk_result.sdk_path
+}
+
+# The tool will print the SDK path on the first line, and the version on the
+# second line.
+find_sdk_lines =
+    exec_script("//build/mac/find_sdk.py", find_sdk_args, "list lines")
+mac_sdk_version = find_sdk_lines[2]
+if (mac_sdk_path == "") {
+  mac_sdk_path = find_sdk_lines[0]
+}
+
+mac_bin_path = find_sdk_lines[1]
+
+# If we're using hermetic Xcode, then we want the paths to be relative so that
+# generated ninja files are independent of the directory location.
+if (!use_system_xcode && !ios_use_goma_rbe) {
+  # If this is called from ios, it is known to point wrong relative path.
+  mac_bin_path = rebase_path(mac_bin_path, root_build_dir)
+}
 
 if (mac_sdk_version != mac_sdk_min &&
     exec_script("//build/check_return_value.py",