Add support of cross-building the engine for ARM64 Linux Host

AUTHORS

@@ -15,4 +15,5 @@ Simon Lightfoot <simon@devangels.london>
 Dwayne Slater <ds84182@gmail.com>
 Tetsuhiro Ueda <najeira@gmail.com>
 shoryukenn <naifu.guan@gmail.com>
-SOTEC GmbH & Co. KG <sotec-contributors@sotec.eu>
+SOTEC GmbH & Co. KG <sotec-contributors@sotec.eu>
+Hidenori Matsubayashi <Hidenori.Matsubayashi@sony.com>

BUILD.gn

@@ -45,14 +45,19 @@ group("flutter") {
     "//flutter/sky",
   ]
 
+  # Flutter SDK artifacts should only be built when either doing host builds, or
+  # for cross-compiled desktop targets.
+  build_engine_artifacts =
+      current_toolchain == host_toolchain || (is_linux && !is_chromeos)
+
   # If enbaled, compile the SDK / snapshot.
   if (!is_fuchsia) {
     public_deps += [
       "//flutter/lib/snapshot:generate_snapshot_bin",
       "//flutter/lib/snapshot:kernel_platform_files",
     ]
 
-    if (current_toolchain == host_toolchain) {
+    if (build_engine_artifacts) {
       public_deps += [
         "//flutter/flutter_frontend_server:frontend_server",
         "//third_party/dart:create_sdk",
@@ -64,8 +69,7 @@ group("flutter") {
     }
   }
 
-  # If on the host, compile tools.
-  if (current_toolchain == host_toolchain) {
+  if (build_engine_artifacts) {
     public_deps += [
       "//flutter/shell/testing",
       "//flutter/tools/const_finder",

DEPS

@@ -616,14 +616,23 @@ hooks = [
     ],
   },
   {
-    'name': 'linux_sysroot',
+    'name': 'linux_sysroot_x64',
     'pattern': '.',
     'condition': 'download_linux_deps',
     'action': [
       'python',
       'src/build/linux/sysroot_scripts/install-sysroot.py',
       '--arch=x64'],
   },
+  {
+    'name': 'linux_sysroot_arm64',
+    'pattern': '.',
+    'condition': 'download_linux_deps',
+    'action': [
+      'python',
+      'src/build/linux/sysroot_scripts/install-sysroot.py',
+      '--arch=arm64'],
+  },
   {
     'name': 'dart package config',
     'pattern': '.',