Remove the current /prefetch switch when relaunching Chrome.

chrome/common/switch_utils.cc

 // Copyright (c) 2011 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 "chrome/common/switch_utils.h"
 
 #include <stddef.h>
 
 #include "base/macros.h"
+#include "build/build_config.h"
 #include "chrome/common/chrome_switches.h"
 
+#if defined(OS_WIN)
+#include "base/strings/string_util.h"
+#endif  // defined(OS_WIN)
+
 namespace switches {
 
+namespace {
+
 // Switches enumerated here will be removed when a background instance of
 // Chrome restarts itself. If your key is designed to only be used once,
 // or if it does not make sense when restarting a background instance to
 // pick up an automatic update, be sure to add it to this list.
 const char* const kSwitchesToRemoveOnAutorestart[] = {
   switches::kApp,
   switches::kAppId,
   switches::kForceFirstRun,
   switches::kMakeDefaultBrowser,
   switches::kNoStartupWindow,
   switches::kRestoreLastSession,
   switches::kShowAppList,
   switches::kWinJumplistAction
 };
 
+}  // namespace
+
 void RemoveSwitchesForAutostart(
     std::map<std::string, base::CommandLine::StringType>* switch_list) {
   for (size_t i = 0; i < arraysize(kSwitchesToRemoveOnAutorestart); ++i)
     switch_list->erase(kSwitchesToRemoveOnAutorestart[i]);
+
+#if defined(OS_WIN)
+  // When Chrome is relaunched, the Windows prefetch profile to use can change
+  // (e.g. a process initially launched in background is relaunched in
+  // foreground). Therefore, always remove Windows prefetch switches from
+  // |switch_list| and let the code building the relaunch command line add a new
+  // one afterwards when appropriate. The format of a Windows prefetch switch is
+  // "/prefetch:#" where # is [1, 8].

[gab, 2016/02/25 20:22:23]

It's never appropriate to re-add one I think as we're always launching a browser
from this.

// The relaunched browser process shouldn't have a /prefetch switch, however
// it's possible the original command-line had one (e.g. a process initially
// launched in background is relaunched in foreground).

(no need to explicitly state that "we'll remove it" either as that's the purpose
of the method and it's thus implicit that if we say "it doesn't belong", we'll
also remove it)

[fdoray, 2016/02/26 18:10:36]

Done. We do need to re-add a switch when a background process is relaunched in
background (background process relaunched in background after an update here
https://code.google.com/p/chromium/codesearch#chromium/src/chrome/browser/bro...)

+  static const char kPrefetchSwitchPrefix[] = "prefetch:";
+  for (auto it = switch_list->lower_bound(kPrefetchSwitchPrefix);
+       it != switch_list->end();) {
+    if (base::StartsWith(it->first, kPrefetchSwitchPrefix,
+                         base::CompareCase::SENSITIVE)) {
+      switch_list->erase(it++);
+    } else {
+      break;
+    }
+  }

[gab, 2016/02/25 20:22:23]

This loop assumes there can be more than one prefetch switch. I don't think this
is necessary and suggest:

static const char kPrefetchSwitchPrefix[] = "prefetch:";
auto it = switch_list->lower_bound(kPrefetchSwitchPrefix);
if (it != switch_list->end() && 
    base::StartsWith(it->first, kPrefetchSwitchPrefix,
                     base::CompareCase::SENSITIVE)) {
  switch_list->erase(it);
}

[fdoray, 2016/02/26 18:10:36]

Done.

+#endif  // defined(OS_WIN)
 }
 
 }  // namespace switches