Initial implementation for sharing field trial state (win)

content/browser/browser_child_process_host_impl.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_child_process_host_impl.h"
 
 #include "base/base_switches.h"
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/debug/dump_without_crashing.h"
@@ skipping 189 matching lines @@
   // Make a copy since the BrowserChildProcessHost dtor mutates the original
   // list.
   BrowserChildProcessList copy = g_child_process_list.Get();
   for (BrowserChildProcessList::iterator it = copy.begin();
        it != copy.end(); ++it) {
     delete (*it)->delegate();  // ~*HostDelegate deletes *HostImpl.
   }
 }
 
 // static
+#if defined(OS_WIN)
+void BrowserChildProcessHostImpl::CopyFeatureAndFieldTrialFlags(
+    base::CommandLine* cmd_line, base::SharedMemory* shared_memory) {
+#else
 void BrowserChildProcessHostImpl::CopyFeatureAndFieldTrialFlags(
     base::CommandLine* cmd_line) {
+#endif
   std::string enabled_features;
   std::string disabled_features;
   base::FeatureList::GetInstance()->GetFeatureOverrides(&enabled_features,
                                                         &disabled_features);
   if (!enabled_features.empty())
     cmd_line->AppendSwitchASCII(switches::kEnableFeatures, enabled_features);
   if (!disabled_features.empty())
     cmd_line->AppendSwitchASCII(switches::kDisableFeatures, disabled_features);
 
   // If we run base::FieldTrials, we want to pass to their state to the
   // child process so that it can act in accordance with each state.
   std::string field_trial_states;
   base::FieldTrialList::AllStatesToString(&field_trial_states);
   if (!field_trial_states.empty()) {
+    // Use shared memory to pass field_trial_states if we're on Windows,
+    // otherwise fallback to the command line.
+#if defined(OS_WIN)
+    size_t length = field_trial_states.size() + 1;
+    shared_memory->CreateAndMapAnonymous(length);
+    memcpy(shared_memory->memory(), field_trial_states.c_str(), length);
+
+    // HANDLE is just typedef'd to void *
+    HANDLE handle = shared_memory->handle().GetHandle();
+    auto uintptr_handle = reinterpret_cast<std::uintptr_t>(handle);
+    std::string string_handle = std::to_string(uintptr_handle);
+    cmd_line->AppendSwitchASCII("field_trial_handle", string_handle);
+    cmd_line->AppendSwitchASCII("field_trial_length", std::to_string(length));
+#else
     cmd_line->AppendSwitchASCII(switches::kForceFieldTrials,
                                 field_trial_states);
+#endif
   }
 }
 
 void BrowserChildProcessHostImpl::Launch(
     SandboxedProcessLauncherDelegate* delegate,
+    base::SharedMemory* field_trial_state,
     base::CommandLine* cmd_line,
     bool terminate_on_shutdown) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
 
   GetContentClient()->browser()->AppendExtraCommandLineSwitches(
       cmd_line, data_.id);
 
   const base::CommandLine& browser_command_line =
       *base::CommandLine::ForCurrentProcess();
   static const char* const kForwardSwitches[] = {
     switches::kDisableLogging,
     switches::kEnableLogging,
     switches::kIPCConnectionTimeout,
     switches::kLoggingLevel,
     switches::kTraceToConsole,
     switches::kV,
     switches::kVModule,
   };
   cmd_line->CopySwitchesFrom(browser_command_line, kForwardSwitches,
                              arraysize(kForwardSwitches));
 
   if (child_connection_) {
     cmd_line->AppendSwitchASCII(switches::kMojoApplicationChannelToken,
                                 child_connection_->service_token());
   }
 
   notify_child_disconnected_ = true;
   child_process_.reset(new ChildProcessLauncher(
       delegate,
+      field_trial_state,
       cmd_line,
       data_.id,
       this,
       child_token_,
       base::Bind(&BrowserChildProcessHostImpl::OnMojoError,
                  weak_factory_.GetWeakPtr(),
                  base::ThreadTaskRunnerHandle::Get()),
       terminate_on_shutdown));
 }
 
@@ skipping 330 matching lines @@
 
 #if defined(OS_WIN)
 
 void BrowserChildProcessHostImpl::OnObjectSignaled(HANDLE object) {
   OnChildDisconnected();
 }
 
 #endif
 
 }  // namespace content