[scheduler] Use Finch to control background throttling.

content/browser/renderer_host/render_view_host_impl.cc

Index: content/browser/renderer_host/render_view_host_impl.cc
diff --git a/content/browser/renderer_host/render_view_host_impl.cc b/content/browser/renderer_host/render_view_host_impl.cc
index 463b5d1e0432dda6abf647fba21089dde042d18f..6cc15f086b5513ad8ba2353615e95ece65994534 100644
--- a/content/browser/renderer_host/render_view_host_impl.cc
+++ b/content/browser/renderer_host/render_view_host_impl.cc
@@ -19,6 +19,7 @@
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/stl_util.h"
+#include "base/strings/string_number_conversions.h"
 #include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/sys_info.h"
@@ -27,6 +28,7 @@
 #include "base/values.h"
 #include "build/build_config.h"
 #include "cc/base/switches.h"
+#include "components/variations/variations_associated_data.h"
 #include "content/browser/bad_message.h"
 #include "content/browser/child_process_security_policy_impl.h"
 #include "content/browser/dom_storage/session_storage_namespace_impl.h"
@@ -413,6 +415,23 @@ void RenderViewHostImpl::SyncRendererPrefs() {
   Send(new ViewMsg_SetRendererPrefs(GetRoutingID(), renderer_preferences));
 }
 
+namespace {
+
+void MaybeSetFloatParameterFromMap(

[ojan, 2016/11/08 19:41:15]

Drive-by pet-peeve nit: I don't feel like this "Maybe" is very valuable. I have
a pet-peeve against our increasing overuse of Maybe in method names, so feel
free to ignore me. Every method with an if-statement in it could be a Maybe
method. Makes the code bloated and hard to read. Better to just never use that
term IMO. SetFloatParameterFromMap is plenty clear IMO. :)

I'd make the same argument about MaybeInitializeBackgroundTimeBudgetPool.
InitializeBackgroundTimeBudgetPool is plenty clear.

[altimin, 2016/11/09 14:46:29]

Done.

+    const std::map<std::string, std::string>& settings,
+    const std::string& setting_name,
+    float* value) {
+  const auto& find_it = settings.find(setting_name);
+  if (find_it == settings.end())
+    return;
+  double parsed_value;
+  if (!base::StringToDouble(find_it->second, &parsed_value))
+    return;
+  *value = parsed_value;
+}
+
+}  // namespace
+
 WebPreferences RenderViewHostImpl::ComputeWebkitPrefs() {
   TRACE_EVENT0("browser", "RenderViewHostImpl::GetWebkitPrefs");
   WebPreferences prefs;
@@ -572,6 +591,23 @@ WebPreferences RenderViewHostImpl::ComputeWebkitPrefs() {
   if (delegate_ && delegate_->HideDownloadUI())
     prefs.hide_download_ui = true;
 
+  std::map<std::string, std::string> expensive_background_throttling_prefs;
+  variations::GetVariationParamsByFeature(

[clamy, 2016/11/09 14:28:51]

We've tried to avoid using things from components inside content/ unless there's
a good reason. What's the reasoning behind this one?

If possible, I would prefer the setting of preferences to match what's done with
all other preferences, for consistency.

[altimin, 2016/11/09 14:46:29]

I didn't find any other cases of plumbing parameters from variations to webkit:
all cases that I know of are binary on/off features which are implemented with
switches and WebRuntimeFeatures. So almost all other preferences here use
switches.

I believe that it's right to use variations component from here, for example,
because GetV8Cache options check for field trial settings with
base::FieldTrialList and variations::GetVariationParams is an extension of that
mechanism. 

[clamy, 2016/11/09 15:27:07]

Acknowledged.

+      features::kExpensiveBackgroundTimerThrottling,
+      &expensive_background_throttling_prefs);
+  MaybeSetFloatParameterFromMap(
+      expensive_background_throttling_prefs, "cpu_budget",
+      &prefs.expensive_background_throttling_cpu_budget);
+  MaybeSetFloatParameterFromMap(
+      expensive_background_throttling_prefs, "initial_budget",
+      &prefs.expensive_background_throttling_initial_budget);
+  MaybeSetFloatParameterFromMap(
+      expensive_background_throttling_prefs, "max_budget",
+      &prefs.expensive_background_throttling_max_budget);
+  MaybeSetFloatParameterFromMap(
+      expensive_background_throttling_prefs, "max_delay",
+      &prefs.expensive_background_throttling_max_delay);
+
   GetContentClient()->browser()->OverrideWebkitPrefs(this, &prefs);
   return prefs;
 }