Add sysroot DEP for standalone builds

Adds sysroot DEPS entries and configures GN to use them. This will make
standalone Dawn builds no longer dependent on locally installed
libraries, instead relying on the sysroot's copy.

NOTE: This is based on bsheedy@'s work:
https://dawn-review.googlesource.com/c/dawn/+/186580

Bug: chromium:336842914
Change-Id: I2b5741630d54bd70ca5fcc539cc6131fa622112d
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/186920
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Antonio Maiorano <amaiorano@google.com>
diff --git a/.gitignore b/.gitignore
index d10d970..4310f96 100644
--- a/.gitignore
+++ b/.gitignore
@@ -6,6 +6,7 @@
 /.gclient_entries
 /.gclient_previous_custom_vars
 /.gclient_previous_sync_commits
+/.gcs_entries
 /.reproxy_cache
 /bazel-*
 /build
diff --git a/.gn b/.gn
index c66bee0..44779cd 100644
--- a/.gn
+++ b/.gn
@@ -46,4 +46,5 @@
       "//third_party/vulkan-deps/vulkan-validation-layers/src"
 
   vma_vulkan_headers_dir = "//third_party/vulkan-deps/vulkan-headers/src"
+  use_sysroot = true
 }
diff --git a/DEPS b/DEPS
index 5f5f53c..e8b4e8b 100644
--- a/DEPS
+++ b/DEPS
@@ -135,6 +135,89 @@
     'dep_type': 'cipd',
   },
 
+  # Linux sysroots for hermetic builds instead of relying on whatever is
+  # available from the system used for compilation. Only applicable to
+  # dawn_standalone since Chromium has its own sysroot copy.
+  'build/linux/debian_bullseye_armhf-sysroot': {
+    'bucket': 'chrome-linux-sysroot',
+    'condition': 'dawn_standalone and checkout_linux and checkout_arm',
+    'dep_type': 'gcs',
+    'objects': [
+      {
+        'object_name': 'e1ace9eea7f5f8906a5de665022abb745efb47ce4931ae774b58005adaf907e9',
+        'sha256sum': 'e1ace9eea7f5f8906a5de665022abb745efb47ce4931ae774b58005adaf907e9',
+        'size_bytes': 96825360,
+        'generation': 1714159610727506,
+      },
+    ],
+  },
+  'build/linux/debian_bullseye_arm64-sysroot': {
+    'bucket': 'chrome-linux-sysroot',
+    'condition': 'dawn_standalone and checkout_linux and checkout_arm64',
+    'dep_type': 'gcs',
+    'objects': [
+      {
+        'object_name': 'd303cf3faf7804c9dd24c9b6b167d0345d41d7fe4bfb7d34add3ab342f6a236c',
+        'sha256sum': 'd303cf3faf7804c9dd24c9b6b167d0345d41d7fe4bfb7d34add3ab342f6a236c',
+        'size_bytes': 103556332,
+        'generation': 1714159596952688,
+      },
+    ],
+  },
+  'build/linux/debian_bullseye_i386-sysroot': {
+    'bucket': 'chrome-linux-sysroot',
+    'condition': 'dawn_standalone and checkout_linux and (checkout_x86 or checkout_x64)',
+    'dep_type': 'gcs',
+    'objects': [
+      {
+        'object_name': '4300851707ad38b204e7f4912950c05ad51da0251ecc4e410de9b9fb94f7decf',
+        'sha256sum': '4300851707ad38b204e7f4912950c05ad51da0251ecc4e410de9b9fb94f7decf',
+        'size_bytes': 116515924,
+        'generation': 1714159579525878,
+      },
+    ],
+  },
+  'build/linux/debian_bullseye_mipsel-sysroot': {
+    'bucket': 'chrome-linux-sysroot',
+    'condition': 'dawn_standalone and checkout_linux and checkout_mips',
+    'dep_type': 'gcs',
+    'objects': [
+      {
+        'object_name': 'cc3202718a58541488e79b0333ce936a32227e07228f6b3c122d99ee45f83270',
+        'sha256sum': 'cc3202718a58541488e79b0333ce936a32227e07228f6b3c122d99ee45f83270',
+        'size_bytes': 93412776,
+        'generation': 1714159559897107,
+      },
+    ],
+  },
+  'build/linux/debian_bullseye_mips64el-sysroot': {
+    'bucket': 'chrome-linux-sysroot',
+    'condition': 'dawn_standalone and checkout_linux and checkout_mips64',
+    'dep_type': 'gcs',
+    'objects': [
+      {
+        'object_name': 'ee94d723b36d1e643820fe7ee2a8f45b3664b4c5d3c3379ebab39e474a2c9f86',
+        'sha256sum': 'ee94d723b36d1e643820fe7ee2a8f45b3664b4c5d3c3379ebab39e474a2c9f86',
+        'size_bytes': 97911708,
+        'generation': 1714159538956875,
+      },
+    ],
+  },
+  'build/linux/debian_bullseye_amd64-sysroot': {
+    'bucket': 'chrome-linux-sysroot',
+    'condition': 'dawn_standalone and checkout_linux and checkout_x64',
+    'dep_type': 'gcs',
+    'objects': [
+      {
+        'object_name': '5df5be9357b425cdd70d92d4697d07e7d55d7a923f037c22dc80a78e85842d2c',
+        'sha256sum': '5df5be9357b425cdd70d92d4697d07e7d55d7a923f037c22dc80a78e85842d2c',
+        'size_bytes': 123084324,
+        'generation': 1714159395960299,
+      },
+    ],
+  },
+
+
   # Testing, GTest and GMock
   'testing': {
     'url': '{chromium_git}/chromium/src/testing@035a9b18047370df7403758b006e6c9696d6b84d',