Linux: Pull and use clang toolchain in third_party

Includes mini_chromium update including one change:
b4128fb Linux GN: support override of clang to different path

Complementary bot change at
https://chromium-review.googlesource.com/c/chromium/tools/build/+/935668.

Bug: crashpad:79, crashpad:220
Change-Id: I9228bf6786d94c34265e933e21e45a899816bb52
Reviewed-on: https://chromium-review.googlesource.com/935470
Reviewed-by: Mark Mentovai <mark@chromium.org>
Commit-Queue: Scott Graham <scottmg@chromium.org>

.gitignore

@@ -15,6 +15,8 @@
 /third_party/fuchsia/qemu
 /third_party/fuchsia/sdk
 /third_party/gtest/gtest
+/third_party/linux/.cipd
+/third_party/linux/clang
 /third_party/gyp/gyp
 /third_party/mini_chromium/mini_chromium
 /third_party/zlib/zlib

DEPS

@@ -14,6 +14,7 @@
 
 vars = {
   'chromium_git': 'https://chromium.googlesource.com',
+  'pull_linux_clang': False
 }
 
 deps = {
@@ -28,7 +29,7 @@ deps = {
       '5e2b3ddde7cda5eb6bc09a5546a76b00e49d888f',
   'crashpad/third_party/mini_chromium/mini_chromium':
       Var('chromium_git') + '/chromium/mini_chromium@' +
-      '4e3b2c0fd5b18832e4221876941111cb12892d3b',
+      'b4128fb9a0684369c9d144a2210496b7583c01a6',
   'crashpad/third_party/zlib/zlib':
       Var('chromium_git') + '/chromium/src/third_party/zlib@' +
       '13dc246a58e4b72104d35f9b1809af95221ebda7',
@@ -115,8 +116,27 @@ hooks = [
   },
   {
     # This uses “cipd install” so that mac-amd64 and linux-amd64 can coexist
-    # peacefully. “cipd ensure” would remove the Linux package when running on a
-    # macOS build host and vice-versa. https://crbug.com/789364.
+    # peacefully. “cipd ensure” would remove the macOS package when running on a
+    # Linux build host and vice-versa. https://crbug.com/789364. This package is
+    # only updated when the solution in .gclient includes an entry like:
+    #   "custom_vars": { "pull_linux_clang": True }
+    'name': 'clang_linux',
+    'pattern': '.',
+    'condition': 'checkout_linux and pull_linux_clang',
+    'action': [
+      'cipd',
+      'install',
+      # sic, using Fuchsia team's generic build of clang for linux-amd64 to
+      # build for linux-amd64 target too.
+      'fuchsia/clang/linux-amd64',
+      'latest',
+      '-root', 'crashpad/third_party/linux/clang/linux-amd64',
+      '-log-level', 'info',
+    ],
+  },
+  {
+    # Same rationale for using "install" rather than "ensure" as for first clang
+    # package. https://crbug.com/789364.
     'name': 'fuchsia_clang_mac',
     'pattern': '.',
     'condition': 'checkout_fuchsia and host_os == "mac"',
@@ -130,9 +150,8 @@ hooks = [
     ],
   },
   {
-    # This uses “cipd install” so that mac-amd64 and linux-amd64 can coexist
-    # peacefully. “cipd ensure” would remove the macOS package when running on a
-    # Linux build host and vice-versa. https://crbug.com/789364.
+    # Same rationale for using "install" rather than "ensure" as for first clang
+    # package. https://crbug.com/789364.
     'name': 'fuchsia_clang_linux',
     'pattern': '.',
     'condition': 'checkout_fuchsia and host_os == "linux"',

third_party/fuchsia/README.crashpad

@@ -1,4 +1,3 @@
 This directory is a placeholder for Fuchsia tools that will be downloaded by
-CIPD (https://github.com/luci/luci-go/tree/master/cipd). The toolchain.ensure
-files specifies which CIPD packages to retrieve, at which versions, and where
-they're stored locally. The CIPD update happens as part of gclient runhooks.
+CIPD (https://github.com/luci/luci-go/tree/master/cipd). The CIPD update happens
+as part of gclient runhooks.

third_party/linux/README.crashpad

@@ -0,0 +1,3 @@
+This directory is a placeholder for Fuchsia tools that will be downloaded by
+CIPD (https://github.com/luci/luci-go/tree/master/cipd). The CIPD update happens
+as part of gclient runhooks.