Wire up ShillSandboxing flag to be enabled by default

In a previous CL:1173260 I meant to wire up this feature flag to be
enabled by default. Somehow I mistakenly landed the code with the
FEATURE_DISABLED_BY_DEFAULT flag instead.

Bug: 649417
Test: Same as CL:1173260
Change-Id: I2154749addb0539be9a2ef53c368d80dc10bee41
Reviewed-on: https://chromium-review.googlesource.com/1190644
Reviewed-by: Mattias Nissler <mnissler@chromium.org>
Commit-Queue: Micah Morton <mortonm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#586444}

chrome/common/chrome_features.cc

@@ -655,7 +655,7 @@ const base::Feature kUsbguard{"USBGuard", base::FEATURE_ENABLED_BY_DEFAULT};
 
 // Enable running shill in a minijail sandbox on Chrome OS.
 const base::Feature kShillSandboxing{"ShillSandboxing",
-                                     base::FEATURE_DISABLED_BY_DEFAULT};
+                                     base::FEATURE_ENABLED_BY_DEFAULT};
 #endif  // defined(OS_CHROMEOS)
 
 // Enable showing a tab-modal dialog while a Web Authentication API request is