Run install-sysroot script before 'gn gen' on PDFium bot

BUG=skia:5727
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2317013002

Review-Url: https://codereview.chromium.org/2317013002

infra/bots/recipe_modules/flavor/pdfium_flavor.py

@@ -24,6 +24,14 @@ class PDFiumFlavorUtils(default_flavor.DefaultFlavorUtils):
         cwd=pdfium_dir,
         **kwargs)
 
+    # Install the sysroot.
+    self.m.run(
+        self.m.step,
+        'sysroot',
+        cmd=['python', 'build/linux/sysroot_scripts/install-sysroot.py',
+             '--arch=amd64'],
+        cwd=pdfium_dir)
+
     # Setup gn args.
     gn_args = [
         'pdf_use_skia=true',

infra/bots/recipes/swarm_compile.expected/Build-Ubuntu-GCC-x86_64-Release-PDFium.json

@@ -95,6 +95,21 @@
     },
     "name": "runhook"
   },
+  {
+    "cmd": [
+      "python",
+      "build/linux/sysroot_scripts/install-sysroot.py",
+      "--arch=amd64"
+    ],
+    "cwd": "[CUSTOM_/_B_WORK]/pdfium",
+    "env": {
+      "BUILDTYPE": "Release",
+      "CHROME_HEADLESS": "1",
+      "PATH": "%(PATH)s:RECIPE_PACKAGE_REPO[depot_tools]:RECIPE_PACKAGE_REPO[depot_tools]",
+      "SKIA_OUT": "[CUSTOM_/_B_WORK]/skia/out/Build-Ubuntu-GCC-x86_64-Release-PDFium"
+    },
+    "name": "sysroot"
+  },
   {
     "cmd": [
       "gn",