Cache --whitelisted-extension-id in SimpleFeature.

During startup, CommandLine::HasSwitch(kWhitelistedExtensionID) is
called ~1000 times by SimpleFeature. It is the most common switch
lookup, the second being kAppsGalleryUpdateUrl at ~300 times.

Caching this avoids allocating and copying the string each time.

BUG=471976

Review URL: https://codereview.chromium.org/1047943002

Cr-Commit-Position: refs/heads/master@{#324583}

2 files changed, 45 insertions, 14 deletions

diff --git a/extensions/common/features/simple_feature.cc b/extensions/common/features/simple_feature.cc
index 34258d4..3322fac 100644
--- a/extensions/common/features/simple_feature.cc
+++ b/extensions/common/features/simple_feature.cc
@@ -11,6 +11,7 @@
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/debug/alias.h"
+#include "base/macros.h"
 #include "base/sha1.h"
 #include "base/stl_util.h"
 #include "base/strings/string_number_conversions.h"
@@ -27,6 +28,10 @@ namespace extensions {
 
 namespace {
 
+// A singleton copy of the --whitelisted-extension-id so that we don't need to
+// copy it from the CommandLine each time.
+std::string* g_whitelisted_extension_id = NULL;
+
 Feature::Availability IsAvailableToManifestForBind(
     const std::string& extension_id,
     Manifest::Type type,
@@ -219,8 +224,33 @@ bool IsCommandLineSwitchEnabled(const std::string& switch_name) {
   return false;
 }
 
+bool IsWhitelistedForTest(const std::string& extension_id) {
+  // TODO(jackhou): Delete the commandline whitelisting mechanism.
+  // Since it is only used it tests, ideally it should not be set via the
+  // commandline. At the moment the commandline is used as a mechanism to pass
+  // the id to the renderer process.
+  if (!g_whitelisted_extension_id) {
+    g_whitelisted_extension_id = new std::string(
+        base::CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
+            switches::kWhitelistedExtensionID));
+  }
+  return !g_whitelisted_extension_id->empty() &&
+         *g_whitelisted_extension_id == extension_id;
+}
+
 }  // namespace
 
+SimpleFeature::ScopedWhitelistForTest::ScopedWhitelistForTest(
+    const std::string& id)
+    : previous_id_(g_whitelisted_extension_id) {
+  g_whitelisted_extension_id = new std::string(id);
+}
+
+SimpleFeature::ScopedWhitelistForTest::~ScopedWhitelistForTest() {
+  delete g_whitelisted_extension_id;
+  g_whitelisted_extension_id = previous_id_;
+}
+
 struct SimpleFeature::Mappings {
   Mappings() {
     extension_types["extension"] = Manifest::TYPE_EXTENSION;
@@ -360,20 +390,9 @@ Feature::Availability SimpleFeature::IsAvailableToManifest(
   if (component_extensions_auto_granted_ && location == Manifest::COMPONENT)
     return CreateAvailability(IS_AVAILABLE, type);
 
-  if (!whitelist_.empty()) {
-    if (!IsIdInWhitelist(extension_id)) {
-      // TODO(aa): This is gross. There should be a better way to test the
-      // whitelist.
-      base::CommandLine* command_line = base::CommandLine::ForCurrentProcess();
-      if (!command_line->HasSwitch(switches::kWhitelistedExtensionID))
-        return CreateAvailability(NOT_FOUND_IN_WHITELIST, type);
-
-      std::string whitelist_switch_value =
-          base::CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
-              switches::kWhitelistedExtensionID);
-      if (extension_id != whitelist_switch_value)
-        return CreateAvailability(NOT_FOUND_IN_WHITELIST, type);
-    }
+  if (!whitelist_.empty() && !IsIdInWhitelist(extension_id) &&
+      !IsWhitelistedForTest(extension_id)) {
+    return CreateAvailability(NOT_FOUND_IN_WHITELIST, type);
   }
 
   if (!MatchesManifestLocation(location))
diff --git a/extensions/common/features/simple_feature.h b/extensions/common/features/simple_feature.h
index 9d8c539..5ec95cf 100644
--- a/extensions/common/features/simple_feature.h
+++ b/extensions/common/features/simple_feature.h
@@ -29,6 +29,18 @@ class SimpleFeatureTest;
 
 class SimpleFeature : public Feature {
  public:
+  // Used by tests to override the cached --whitelisted-extension-id.
+  class ScopedWhitelistForTest {
+   public:
+    explicit ScopedWhitelistForTest(const std::string& id);
+    ~ScopedWhitelistForTest();
+
+   private:
+    std::string* previous_id_;
+
+    DISALLOW_COPY_AND_ASSIGN(ScopedWhitelistForTest);
+  };
+
   SimpleFeature();
   ~SimpleFeature() override;