     self.explicitTests = explicitTests
     self.additionalBuildTargets = additionalBuildTargets
 
+    var envVars: [String: String]
+    if let launchActionEnvVars = launchActionEnvVars {
+      envVars = launchActionEnvVars
+    } else {
+      envVars = [:]
+    }
+
+    // Disable OS_ACTIVITY_MODE by default to cut down on Xcode 8 logging.
+    // b/31544656
+    if envVars["OS_ACTIVITY_MODE"] == nil {
+      envVars["OS_ACTIVITY_MODE"] = "disable"
+    }
+    self.launchActionEnvVars = envVars
+
     primaryTargetBuildableReference = BuildableReference(target: target,
                                                          projectBundleName: projectBundleName)
   }

  let additionalBuildTargets: [(PBXTarget, String)]?

  let primaryTargetBuildableReference: BuildableReference

  init(target: PBXTarget,
       project: PBXProject,

       runnableDebuggingMode: RunnableDebuggingMode = .Default,
       version: String = "1.3",
       explicitTests: [PBXTarget]? = nil,
       additionalBuildTargets: [(PBXTarget, String)]? = nil,
       launchActionEnvVars: [String: String]? = nil) {
    self.version = version
    self.target = target
    self.project = project
