Fix missing build dependency in //chrome/services/isolated_xr_device:lib

Chrome/services/isolated_xr_device depends on a feature flag in chrome/common.
chrome/common/chrome_features.h then includes chrome/common/buildflags.h.
Sometimes buildflags.h isn't available when isolated_xr_device is built.

The fix is to add a dependency.

BUG=892836

Change-Id: I225dfff4158d7eca7f79ee54f5305a27eae71065
Reviewed-on: https://chromium-review.googlesource.com/c/1266596Reviewed-by: Bill Orr <billorr@chromium.org>
Reviewed-by: Marijn Kruisselbrink <mek@chromium.org>
Reviewed-by: Brian Sheedy <bsheedy@chromium.org>
Commit-Queue: Bill Orr <billorr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#597626}

chrome/services/isolated_xr_device/BUILD.gn

@@ -19,6 +19,7 @@ source_set("lib") {
 
   deps = [
     "//base",
+    "//chrome/common",
     "//device/vr:vr",
     "//device/vr/public/mojom",
     "//device/vr/public/mojom:test_mojom",