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 190 matching lines @@
   // 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
 void BrowserChildProcessHostImpl::CopyFeatureAndFieldTrialFlags(
-    base::CommandLine* cmd_line) {
+    base::CommandLine* cmd_line,
+    base::SharedMemory* shared_memory) {
   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()) {
-    cmd_line->AppendSwitchASCII(switches::kForceFieldTrials,
-                                field_trial_states);
+    // Use shared memory to pass field_trial_states if we can, otherwise
+    // fallback to the command line.
+    if (shared_memory) {
+      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 *
+      auto uintptr_handle =
+          reinterpret_cast<std::uintptr_t>(shared_memory->handle().GetHandle());
+      std::string field_trial_handle =
+          std::to_string(uintptr_handle) + "," + std::to_string(length);
+
+      cmd_line->AppendSwitchASCII(switches::kFieldTrialHandle,
+                                  field_trial_handle);
+    } else {
+      cmd_line->AppendSwitchASCII(switches::kForceFieldTrials,
+                                  field_trial_states);
+    }
   }
 }
 
 void BrowserChildProcessHostImpl::Launch(
     SandboxedProcessLauncherDelegate* delegate,
     base::CommandLine* cmd_line,
+    const base::SharedMemory* field_trial_state,
     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,
-      cmd_line,
-      data_.id,
-      this,
-      child_token_,
+      delegate, cmd_line, data_.id, this, field_trial_state, child_token_,
       base::Bind(&BrowserChildProcessHostImpl::OnMojoError,
                  weak_factory_.GetWeakPtr(),
                  base::ThreadTaskRunnerHandle::Get()),
       terminate_on_shutdown));
 }
 
 const ChildProcessData& BrowserChildProcessHostImpl::GetData() const {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
   return data_;
 }
@@ skipping 326 matching lines @@
 
 #if defined(OS_WIN)
 
 void BrowserChildProcessHostImpl::OnObjectSignaled(HANDLE object) {
   OnChildDisconnected();
 }
 
 #endif
 
 }  // namespace content