[Extensions Cleanup] Constify extensions in api_unittest

In practice, Extension objects are pretty much always const. Update
extensions/browser/api_unittest.h to use const Extension objects, rather
than mutable ones.

Bug: 889925
Change-Id: I7e13dac4376eb0e358a30e2fe49154976f02fb0d
Reviewed-on: https://chromium-review.googlesource.com/1252008Reviewed-by: Karan Bhatia <karandeepb@chromium.org>
Commit-Queue: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595200}

extensions/browser/api/alarms/alarms_api_unittest.cc

@@ -642,7 +642,7 @@ TEST_F(ExtensionAlarmsSchedulingTest, DifferentMinimumGranularities) {
   // Create a new extension, which is packed, and has a granularity of 1 minute.
   // CreateAlarm() uses extension_, so keep a ref of the old one around, and
   // repopulate extension_.
-  scoped_refptr<Extension> extension2(extension_ref());
+  scoped_refptr<const Extension> extension2(extension_ref());
   set_extension(
       utils::CreateEmptyExtensionWithLocation(extensions::Manifest::INTERNAL));
 

extensions/browser/api_unittest.h

@@ -39,8 +39,8 @@ class ApiUnitTest : public ExtensionsTest {
 
   content::WebContents* contents() { return contents_.get(); }
   const Extension* extension() const { return extension_.get(); }
-  scoped_refptr<Extension> extension_ref() { return extension_; }
-  void set_extension(scoped_refptr<Extension> extension) {
+  scoped_refptr<const Extension> extension_ref() { return extension_; }
+  void set_extension(scoped_refptr<const Extension> extension) {
     extension_ = extension;
   }
 
@@ -92,7 +92,7 @@ class ApiUnitTest : public ExtensionsTest {
   std::unique_ptr<content::WebContents> contents_;
 
   // The Extension used when running API function calls.
-  scoped_refptr<Extension> extension_;
+  scoped_refptr<const Extension> extension_;
 };
 
 }  // namespace extensions