Add a switch for faking channels for Variations filtering.

chrome/browser/metrics/variations/variations_service.cc

Index: chrome/browser/metrics/variations/variations_service.cc
diff --git a/chrome/browser/metrics/variations/variations_service.cc b/chrome/browser/metrics/variations/variations_service.cc
index b4e12da5b1bb716dbe4b3ddb0f88b9d6b3ae6461..2c3ce903aa460b940fd8b3da973b8c8818077b40 100644
--- a/chrome/browser/metrics/variations/variations_service.cc
+++ b/chrome/browser/metrics/variations/variations_service.cc
@@ -60,6 +60,31 @@ chrome::VersionInfo::Channel ConvertStudyChannelToVersionChannel(
   return chrome::VersionInfo::CHANNEL_UNKNOWN;
 }
 
+// Wrapper around channel checking, used to enable channel mocking for
+// testing. If the current browser channel is not UNKNOWN, this will return
+// that channel value. Otherwise, if the fake channel flag is provided, this
+// will return the fake channel. Failing that, this will return the UNKNOWN
+// channel.
+chrome::VersionInfo::Channel GetChannelForVariations() {
+  chrome::VersionInfo::Channel channel = chrome::VersionInfo::GetChannel();
+  if (channel != chrome::VersionInfo::CHANNEL_UNKNOWN)
+    return channel;
+  std::string forced_channel =
+      CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
+          switches::kFakeVariationsChannel);
+  if (forced_channel == "stable")
+    channel = chrome::VersionInfo::CHANNEL_STABLE;
+  else if (forced_channel == "beta")
+    channel = chrome::VersionInfo::CHANNEL_BETA;
+  else if (forced_channel == "dev")
+    channel = chrome::VersionInfo::CHANNEL_DEV;
+  else if (forced_channel == "canary")
+    channel = chrome::VersionInfo::CHANNEL_CANARY;
+  else
+    DVLOG(1) << "Invalid channel provided: " << forced_channel;
+  return channel;
+}
+
 Study_Platform GetCurrentPlatform() {
 #if defined(OS_WIN)
   return Study_Platform_PLATFORM_WINDOWS;
@@ -282,7 +307,7 @@ bool VariationsService::ShouldAddStudy(
     const chrome::VersionInfo& version_info,
     const base::Time& reference_date) {
   if (study.has_filter()) {
-    if (!CheckStudyChannel(study.filter(), chrome::VersionInfo::GetChannel())) {

[Alexei Svitkine (slow), 2013/01/04 20:17:34]

VariationsService::CreateTrialsFromSeed() calls this for each study in the seed.
I suggest making the channel a param to ShouldAddStudy() to avoid doing the
command-line parsing for every study.

Alternatively, we could do the command-line parsing only once and store the
resulting chrome::VersionInfo::Channel as a field on the variations_service
(though, that will still need to be passed as a param, since this is a static
function).

+    if (!CheckStudyChannel(study.filter(), GetChannelForVariations())) {
       DVLOG(1) << "Filtered out study " << study.name() << " due to channel.";
       return false;
     }