[Video Capture Service] Add secondary feature flag as a kill switch

Adds a new secondary base::Feature for controlling whether or not
the video capture service is enabled. This gets enabled by default
and serves as a kill switch for groups of devices that force the
primary switch enabled via command-line argument.

Design Doc: https://docs.google.com/document/d/1n9I_DfuNGIA7PUWHOX2O2HVnI1d87q7W7lNTqVZkm0Y/edit?usp=sharing

Bug: 870819
Change-Id: Idd861e838f12a72b54e1140bc3fc613ee5b53018
Reviewed-on: https://chromium-review.googlesource.com/1168001
Commit-Queue: Christian Fremerey <chfremer@chromium.org>
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583847}

content/public/common/content_features.cc

@@ -271,6 +271,13 @@ const base::Feature kMojoVideoCapture {
 #endif
 };
 
+// A secondary switch used in combination with kMojoVideoCapture.
+// This is intended as a kill switch to allow disabling the service on
+// particular groups of devices even if they forcibly enable kMojoVideoCapture
+// via a command-line argument.
+const base::Feature kMojoVideoCaptureSecondary{
+    "MojoVideoCaptureSecondary", base::FEATURE_ENABLED_BY_DEFAULT};
+
 // If the network service is enabled, runs it in process.
 const base::Feature kNetworkServiceInProcess{"NetworkServiceInProcess",
                                              base::FEATURE_DISABLED_BY_DEFAULT};
@@ -691,8 +698,13 @@ enum class VideoCaptureServiceConfiguration {
   kDisabled
 };
 
+bool ShouldEnableVideoCaptureService() {
+  return base::FeatureList::IsEnabled(features::kMojoVideoCapture) &&
+         base::FeatureList::IsEnabled(features::kMojoVideoCaptureSecondary);
+}
+
 VideoCaptureServiceConfiguration GetVideoCaptureServiceConfiguration() {
-  if (!base::FeatureList::IsEnabled(features::kMojoVideoCapture))
+  if (!ShouldEnableVideoCaptureService())
     return VideoCaptureServiceConfiguration::kDisabled;
 
 #if defined(OS_ANDROID)

content/public/common/content_features.h

@@ -69,6 +69,7 @@ CONTENT_EXPORT extern const base::Feature kModuleScriptsDynamicImport;
 CONTENT_EXPORT extern const base::Feature kModuleScriptsImportMetaUrl;
 CONTENT_EXPORT extern const base::Feature kMojoSessionStorage;
 CONTENT_EXPORT extern const base::Feature kMojoVideoCapture;
+CONTENT_EXPORT extern const base::Feature kMojoVideoCaptureSecondary;
 CONTENT_EXPORT extern const base::Feature kNetworkServiceInProcess;
 CONTENT_EXPORT extern const base::Feature kNotificationContentImage;
 CONTENT_EXPORT extern const base::Feature kOriginPolicy;