Remove the current /prefetch switch when relaunching Chrome.

chrome/common/switch_utils.cc

Index: chrome/common/switch_utils.cc
diff --git a/chrome/common/switch_utils.cc b/chrome/common/switch_utils.cc
index 1b0f6c6cf752ad8612a4f923fdaa60a227167e8e..742e0a92d95c8995beba40582dd8e99806ace531 100644
--- a/chrome/common/switch_utils.cc
+++ b/chrome/common/switch_utils.cc
@@ -7,10 +7,17 @@
 #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
@@ -26,10 +33,31 @@ const char* const kSwitchesToRemoveOnAutorestart[] = {
   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