Make sysroot injectable.

With this CL, we can inject sysroot precisely.

BUG=1043804
TEST=Built locally.

Change-Id: I459a45eca86f96c4b143b055b588cd50e24f283a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2057503
Commit-Queue: Hidehiko Abe <hidehiko@chromium.org>
Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#741566}

build/config/sysroot.gni

@@ -8,27 +8,34 @@
 import("//build/config/chrome_build.gni")
 
 declare_args() {
-  # The absolute path of the sysroot that is applied when compiling using
-  # the target toolchain.
+  # The path of the sysroot that is applied when compiling using the target
+  # toolchain.
   target_sysroot = ""
 
-  # The absolute path to directory containing linux sysroot images
+  # The path to directory containing linux sysroot images.
   target_sysroot_dir = "//build/linux"
 
+  # The path of the sysroot for the current toolchain. If empty, default
+  # sysroot is used.
+  sysroot = ""
+
+  # Controls default is_linux sysroot. If set to true, and sysroot
+  # is empty, default sysroot is calculated.
   use_sysroot = current_cpu == "x86" || current_cpu == "x64" ||
                 current_cpu == "arm" || current_cpu == "arm64" ||
                 current_cpu == "mipsel" || current_cpu == "mips64el"
 }
 
-if (current_os == target_os && current_cpu == target_cpu &&
+if (sysroot == "") {
+  if (current_os == target_os && current_cpu == target_cpu &&
       target_sysroot != "") {
     sysroot = target_sysroot
-} else if (is_android) {
+  } else if (is_android) {
     import("//build/config/android/config.gni")
 
     # Android uses unified headers, and thus a single compile time sysroot
     sysroot = "$android_toolchain_root/sysroot"
-} else if (is_linux && use_sysroot) {
+  } else if (is_linux && use_sysroot) {
     # By default build against a sysroot image downloaded from Cloud Storage
     # during gclient runhooks.
     if (current_cpu == "x64") {
@@ -60,19 +67,16 @@ if (current_os == target_os && current_cpu == target_cpu &&
                       "string") == "True",
           "Missing sysroot ($sysroot). To fix, run: build/linux/sysroot_scripts/install-sysroot.py --arch=$_script_arch")
     }
-} else if (is_mac) {
+  } else if (is_mac) {
     import("//build/config/mac/mac_sdk.gni")
     sysroot = mac_sdk_path
-} else if (is_ios) {
+  } else if (is_ios) {
     import("//build/config/ios/ios_sdk.gni")
     sysroot = ios_sdk_path
-} else if (is_fuchsia) {
+  } else if (is_fuchsia) {
     import("//build/config/fuchsia/config.gni")
     if (current_cpu == "arm64" || current_cpu == "x64") {
       sysroot = fuchsia_sdk + "/arch/$current_cpu/sysroot"
-  } else {
-    sysroot = ""
     }
-} else {
-  sysroot = ""
+  }
 }

build/toolchain/cros/BUILD.gn

@@ -69,6 +69,7 @@ cros_toolchain("target") {
     use_debug_fission = use_debug_fission
     use_gold = use_gold
     use_sysroot = use_sysroot
+    sysroot = target_sysroot
   }
 }
 
@@ -132,6 +133,7 @@ cros_toolchain("host") {
     current_cpu = host_cpu
     current_os = "linux"
     use_sysroot = use_sysroot
+    sysroot = cros_host_sysroot
   }
 }
 
@@ -166,5 +168,6 @@ cros_toolchain("v8_snapshot") {
     v8_current_cpu = v8_target_cpu
     current_os = "linux"
     use_sysroot = use_sysroot
+    sysroot = cros_v8_snapshot_sysroot
   }
 }

build/toolchain/cros_toolchain.gni

@@ -61,6 +61,7 @@ declare_args() {
   cros_host_extra_cppflags = ""
   cros_host_extra_cxxflags = ""
   cros_host_extra_ldflags = ""
+  cros_host_sysroot = ""
 
   cros_v8_snapshot_ar = "${clang_base_path}/bin/llvm-ar"
   cros_v8_snapshot_cc = "${clang_base_path}/bin/clang"
@@ -72,6 +73,7 @@ declare_args() {
   cros_v8_snapshot_extra_cppflags = ""
   cros_v8_snapshot_extra_cxxflags = ""
   cros_v8_snapshot_extra_ldflags = ""
+  cros_v8_snapshot_sysroot = ""
 
   cros_nacl_bootstrap_extra_cflags = ""
   cros_nacl_bootstrap_extra_cppflags = ""