Stop injection when injections are invalidated

extensions/renderer/user_script_injector.cc

Index: extensions/renderer/user_script_injector.cc
diff --git a/extensions/renderer/user_script_injector.cc b/extensions/renderer/user_script_injector.cc
index 1910548ba24b340d720cd7eb4ea16d8af38e6416..88b43ada616d5f1b8cb4eec499689185c92b9bdc 100644
--- a/extensions/renderer/user_script_injector.cc
+++ b/extensions/renderer/user_script_injector.cc
@@ -139,13 +139,15 @@ bool UserScriptInjector::ExpectsResults() const {
 
 bool UserScriptInjector::ShouldInjectJs(
     UserScript::RunLocation run_location) const {
-  return script_ && script_->run_location() == run_location &&
+  CHECK(script_);
+  return script_->run_location() == run_location &&
          !script_->js_scripts().empty();
 }
 
 bool UserScriptInjector::ShouldInjectCss(
     UserScript::RunLocation run_location) const {
-  return script_ && run_location == UserScript::DOCUMENT_START &&
+  CHECK(script_);
+  return run_location == UserScript::DOCUMENT_START &&
          !script_->css_scripts().empty();
 }
 
@@ -153,10 +155,7 @@ PermissionsData::AccessType UserScriptInjector::CanExecuteOnFrame(
     const InjectionHost* injection_host,
     blink::WebLocalFrame* web_frame,
     int tab_id) const {
-  // There is no harm in allowing the injection when the script is gone,
-  // because there is nothing to inject.
-  if (!script_)
-    return PermissionsData::ACCESS_ALLOWED;
+  CHECK(script_);
 
   if (script_->consumer_instance_type() ==
           UserScript::ConsumerInstanceType::WEBVIEW) {
@@ -198,14 +197,12 @@ PermissionsData::AccessType UserScriptInjector::CanExecuteOnFrame(
 
 std::vector<blink::WebScriptSource> UserScriptInjector::GetJsSources(
     UserScript::RunLocation run_location) const {
-  std::vector<blink::WebScriptSource> sources;
-  if (!script_)
-    return sources;
-
+  CHECK(script_);
   DCHECK_EQ(script_->run_location(), run_location);
 
   const UserScript::FileList& js_scripts = script_->js_scripts();
 
+  std::vector<blink::WebScriptSource> sources;
   for (UserScript::FileList::const_iterator iter = js_scripts.begin();
        iter != js_scripts.end();
        ++iter) {
@@ -232,11 +229,9 @@ std::vector<blink::WebScriptSource> UserScriptInjector::GetJsSources(
 std::vector<std::string> UserScriptInjector::GetCssSources(
     UserScript::RunLocation run_location) const {
   DCHECK_EQ(UserScript::DOCUMENT_START, run_location);
+  CHECK(script_);
 
   std::vector<std::string> sources;
-  if (!script_)
-    return sources;
-
   const UserScript::FileList& css_scripts = script_->css_scripts();
   for (UserScript::FileList::const_iterator iter = css_scripts.begin();
        iter != css_scripts.end();
@@ -249,8 +244,7 @@ std::vector<std::string> UserScriptInjector::GetCssSources(
 void UserScriptInjector::GetRunInfo(
     ScriptsRunInfo* scripts_run_info,
     UserScript::RunLocation run_location) const {
-  if (!script_)
-    return;
+  CHECK(script_);
 
   if (ShouldInjectJs(run_location)) {
     const UserScript::FileList& js_scripts = script_->js_scripts();