Whitelist V4L2 devices on Chromecast

Some video paths go through the V4L2 decoder, so need to whitelist it to
work with the early sandbox.

Bug: b/113126106
Test: Compiled
Change-Id: Iae5f144efa2b2017d8a6c0e55dfc4128bbd65ce4
Reviewed-on: https://chromium-review.googlesource.com/1199708Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Jorge Lucangeli Obes <jorgelo@chromium.org>
Commit-Queue: Daniel Nicoara <dnicoara@chromium.org>
Cr-Commit-Position: refs/heads/master@{#589222}

content/gpu/gpu_sandbox_hook_linux.cc

@@ -237,9 +237,14 @@ std::vector<BrokerFilePermission> FilePermissionsForGpu(
     }
   }
 
-  if (UseChromecastSandboxWhitelist() && IsArchitectureArm()) {
-    AddChromecastArmGpuWhitelist(&permissions);
-    return permissions;
+  if (UseChromecastSandboxWhitelist()) {
+    if (UseV4L2Codec())
+      AddV4L2GpuWhitelist(&permissions, options);
+
+    if (IsArchitectureArm()) {
+      AddChromecastArmGpuWhitelist(&permissions);
+      return permissions;
+    }
   }
 
   AddStandardGpuWhiteList(&permissions);