Enable features API for content shell and webview

content/browser/browser_main_loop.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/browser_main_loop.h"
 
 #include <stddef.h>
 #include <utility>
 
 #include "base/bind.h"
@@ skipping 677 matching lines @@
 
 int BrowserMainLoop::PreCreateThreads() {
   if (parts_) {
     TRACE_EVENT0("startup",
         "BrowserMainLoop::CreateThreads:PreCreateThreads");
     TRACK_SCOPED_REGION("Startup", "BrowserMainLoop::PreCreateThreads");
 
     result_code_ = parts_->PreCreateThreads();
   }
 
-  // Initialize an instance of FeatureList. This will be a no-op if an instance
-  // was already set up by the embedder.
-  base::FeatureList::InitializeInstance();
+  // Initialize from command line flags only if we haven't yet.

[no sievers, 2016/03/30 18:36:03]

nit: the 'only if we haven't yet' comment does not match the code. Did you mean
it's safe to call this repeatedly and it does nothing the second time?

[Changwan Ryu, 2016/03/31 00:31:44]

Updated the comment.

+  const base::CommandLine* command_line =
+      base::CommandLine::ForCurrentProcess();
+  base::FeatureList::InitializeInstance(
+      command_line->GetSwitchValueASCII(switches::kEnableFeatures),
+      command_line->GetSwitchValueASCII(switches::kDisableFeatures));
 
   // TODO(chrisha): Abstract away this construction mess to a helper function,
   // once MemoryPressureMonitor is made a concrete class.
 #if defined(OS_CHROMEOS)
   if (chromeos::switches::MemoryPressureHandlingEnabled()) {
     memory_pressure_monitor_.reset(new base::chromeos::MemoryPressureMonitor(
         chromeos::switches::GetMemoryPressureThresholds()));
   }
 #elif defined(OS_MACOSX)
   memory_pressure_monitor_.reset(new base::mac::MemoryPressureMonitor());
@@ skipping 732 matching lines @@
   DCHECK(is_tracing_startup_for_duration_);
 
   is_tracing_startup_for_duration_ = false;
   TracingController::GetInstance()->StopTracing(
       TracingController::CreateFileSink(
           startup_trace_file_,
           base::Bind(OnStoppedStartupTracing, startup_trace_file_)));
 }
 
 }  // namespace content