Control TaskScheduler initialization params in renderers via field trial.

components/task_scheduler_util/common/variations_util.cc

Index: components/task_scheduler_util/common/variations_util.cc
diff --git a/components/task_scheduler_util/common/variations_util.cc b/components/task_scheduler_util/common/variations_util.cc
index bc072a208ce40112fa6b23f4fb761f5edaa56ecd..96119591f9bde3a097b11ae625ba4149db5ed8e2 100644
--- a/components/task_scheduler_util/common/variations_util.cc
+++ b/components/task_scheduler_util/common/variations_util.cc
@@ -4,10 +4,12 @@
 
 #include "components/task_scheduler_util/common/variations_util.h"
 
+#include "base/command_line.h"
 #include "base/logging.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_piece.h"
 #include "base/strings/string_split.h"
+#include "base/strings/string_util.h"
 #include "base/task_scheduler/initialization_util.h"
 #include "base/time/time.h"
 
@@ -15,6 +17,15 @@ namespace task_scheduler_util {
 
 namespace {
 
+constexpr char kTaskSchedulerVariationParamsSwitch[] =
+    "task-scheduler-variation-params";
+
+constexpr char kSeparator[] = "|";
+
+bool ContainsSeparator(const std::string& str) {
+  return str.find(kSeparator) != std::string::npos;
+}
+
 struct SchedulerVariableWorkerPoolParams {
   base::SchedulerWorkerPoolParams::StandbyThreadPolicy standby_thread_policy;
   int max_threads = 0;
@@ -105,4 +116,51 @@ std::vector<base::SchedulerWorkerPoolParams> GetWorkerPoolParams(
   return worker_pool_params_vector;
 }
 
+void AddVariationParamsToCommandLine(
+    const std::map<std::string, std::string> variation_params,
+    base::StringPiece key_prefix,
+    base::CommandLine* command_line) {
+  DCHECK(command_line);
+
+  std::vector<std::string> parts;
+  for (const auto& key_value : variation_params) {
+    if (base::StartsWith(key_value.first, key_prefix,
+                         base::CompareCase::SENSITIVE)) {
+      if (ContainsSeparator(key_value.first) ||

[gab, 2016/12/12 17:33:33]

Wrap in #if DCHECK_IS_ON() and NOTREACHED() instead of DLOG (I think it's fine
to assume in non-DCHECK builds that we're getting sane data from the server)

[fdoray, 2016/12/12 18:38:26]

Are you sure? "Things like disk corruption or strange network errors are
examples of exceptional circumstances that nevertheless should not result in
DCHECK() failure."
https://chromium.googlesource.com/chromium/src/+/master/styleguide/c++/c++.md...

If so, should we also stop handling errors in
https://cs.chromium.org/chromium/src/components/task_scheduler_util/variation...
?

[gab, 2016/12/13 20:00:00]

But here, you're doing the encoding, right? It's not from disk or network? If
the config from network is borked, it's up to Finch to verify this, not us,
right?

[robliao, 2017/01/03 08:00:01]

While we're doing the encoding, we should still be robust to misconfiguration.
If we misconfigure finch (or worse, someone uses a finch based attack vector),
we should immediately reject the config.

+          ContainsSeparator(key_value.second)) {
+        DLOG(ERROR)
+            << "Unexpected Character in Task Scheduler Variation Params: "
+            << key_value.first << " [" << key_value.second << "]";
+        return;
+      }
+      parts.push_back(key_value.first);
+      parts.push_back(key_value.second);
+    }
+  }
+
+  if (!parts.empty()) {
+    command_line->AppendSwitchASCII(kTaskSchedulerVariationParamsSwitch,
+                                    base::JoinString(parts, kSeparator));
+  }
+}
+
+std::map<std::string, std::string> GetVariationParamsFromCommandLine(
+    const base::CommandLine& command_line) {
+  const auto serialized_variation_params =
+      command_line.GetSwitchValueASCII(kTaskSchedulerVariationParamsSwitch);
+  const auto parts =
+      base::SplitStringPiece(serialized_variation_params, kSeparator,
+                             base::KEEP_WHITESPACE, base::SPLIT_WANT_NONEMPTY);
+  std::map<std::string, std::string> variation_params;
+  for (auto it = parts.begin(); it != parts.end(); ++it) {
+    auto key = *it;

[gab, 2016/12/12 17:33:33]

const&

[gab, 2017/01/05 18:40:05]

ping

[fdoray, 2017/01/06 17:29:03]

This is a StringPiece. Changed auto -> StringPiece to be more explicit.

+    ++it;
+    if (it == parts.end())
+      return std::map<std::string, std::string>();

[gab, 2016/12/12 17:33:33]

NOTREACHED()

[robliao, 2017/01/03 08:00:01]

Command Lines aren't necessarily a safe data stream, so validating the input
here is appropriate.

[gab, 2017/01/05 18:40:05]

Sure but there's something seriously wrong if this fails and a developer should
be warned via a NOTREACHED() IMO (I'm okay deviating slightly from the
"NOTREACHED() means cannot be reached ever" here because this is not
typical/expected edge case error handling).

[fdoray, 2017/01/06 17:29:03]

Done.

+    auto value = *it;

[gab, 2016/12/12 17:33:33]

const&

[gab, 2017/01/05 18:40:05]

ping

[fdoray, 2017/01/06 17:29:03]

This is a StringPiece. Changed auto -> StringPiece to be more explicit.

+    variation_params[key.as_string()] = value.as_string();
+  }
+  return variation_params;
+}
+
 }  // namespace task_scheduler_util