Add Fuchsia platform deps

Bug: b/232740856
Change-Id: Ia0c14753262f2d66e2bb2aa794ecf5124a016835
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/275520
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Christoffer Jansson <jansson@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#38175}

DEPS

@@ -21,6 +21,10 @@ vars = {
   # By default, download the fuchsia sdk from the public sdk directory.
   'fuchsia_sdk_cipd_prefix': 'fuchsia/sdk/gn/',
   'fuchsia_version': 'version:9.20220919.2.1',
+  # By default, download the fuchsia images from the fuchsia GCS bucket.
+  'fuchsia_images_bucket': 'fuchsia',
+  'checkout_fuchsia_boot_images': "qemu.x64",
+  'checkout_fuchsia': False,
 
   # By default, do not check out the re-client binaries.
   'checkout_reclient': False,
@@ -2319,6 +2323,17 @@ hooks = [
     'condition': 'checkout_mac',
     'action': ['python3', 'src/build/mac_toolchain.py'],
   },
+  {
+    'name': 'Download Fuchsia system images',
+    'pattern': '.',
+    'condition': 'checkout_fuchsia',
+    'action': [
+      'python3',
+      'src/build/fuchsia/update_images.py',
+      '--boot-images={checkout_fuchsia_boot_images}',
+      '--default-bucket={fuchsia_images_bucket}',
+    ],
+  },
   {
     # Note: On Win, this should run after win_toolchain, as it may use it.
     'name': 'clang',

webrtc.gni

@@ -35,6 +35,10 @@ if (is_mac) {
   import("//build/config/mac/rules.gni")
 }
 
+if (is_fuchsia) {
+  import("//build/config/fuchsia/config.gni")
+}
+
 # This declare_args is separated from the next one because args declared
 # in this one, can be read from the next one (args defined in the same
 # declare_args cannot be referenced in that scope).