Split content script injections into multiple tasks

extensions/renderer/script_injection_manager.cc

Index: extensions/renderer/script_injection_manager.cc
diff --git a/extensions/renderer/script_injection_manager.cc b/extensions/renderer/script_injection_manager.cc
index 1e872e245909748d0ffef6b0814f5ea2117c400c..7c51400233ddd5f0a8dcaf265f647d041acd70ad 100644
--- a/extensions/renderer/script_injection_manager.cc
+++ b/extensions/renderer/script_injection_manager.cc
@@ -20,6 +20,7 @@
 #include "extensions/common/extension.h"
 #include "extensions/common/extension_messages.h"
 #include "extensions/common/extension_set.h"
+#include "extensions/common/feature_switch.h"
 #include "extensions/renderer/extension_frame_helper.h"
 #include "extensions/renderer/extension_injection_host.h"
 #include "extensions/renderer/programmatic_script_injector.h"
@@ -189,15 +190,23 @@ void ScriptInjectionManager::RFOHelper::DidFinishDocumentLoad() {
       base::Bind(&ScriptInjectionManager::RFOHelper::RunIdle,
                  weak_factory_.GetWeakPtr()),
       base::TimeDelta::FromMilliseconds(kScriptIdleTimeoutInMs));
+
+  if (FeatureSwitch::yield_between_content_script_runs()->IsEnabled()) {

[Devlin, 2017/03/02 02:33:17]

IsEnabled() is non-trivial - let's cache the result somewhere

[Kunihiko Sakamoto, 2017/03/06 09:11:05]

Added cache to FeatureSwitch class.
(ScriptInjection::InjectJs() uses this flag too, so we'd have to pass around the
value otherwise.)

+    ExtensionFrameHelper::Get(render_frame())->ScheduleAtDocumentIdle(
+        base::Bind(&ScriptInjectionManager::RFOHelper::RunIdle,
+                   weak_factory_.GetWeakPtr()));
+  }
 }
 
 void ScriptInjectionManager::RFOHelper::DidFinishLoad() {
   DCHECK(content::RenderThread::Get());
-  // Ensure that we don't block any UI progress by running scripts.
-  base::ThreadTaskRunnerHandle::Get()->PostTask(
-      FROM_HERE,
-      base::Bind(&ScriptInjectionManager::RFOHelper::RunIdle,
-                 weak_factory_.GetWeakPtr()));
+  if (!FeatureSwitch::yield_between_content_script_runs()->IsEnabled()) {
+    // Ensure that we don't block any UI progress by running scripts.
+    base::ThreadTaskRunnerHandle::Get()->PostTask(
+        FROM_HERE,
+        base::Bind(&ScriptInjectionManager::RFOHelper::RunIdle,
+                   weak_factory_.GetWeakPtr()));
+  }
 }
 
 void ScriptInjectionManager::RFOHelper::FrameDetached() {