Enforce the 'requirements' field in manifests.

chrome/browser/extensions/requirements_checker.h

+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_BROWSER_EXTENSIONS_REQUIREMENTS_CHECKER_H_
+#define CHROME_BROWSER_EXTENSIONS_REQUIREMENTS_CHECKER_H_
+
+#include <vecotr>

[Aaron Boodman, 2012/07/30 12:15:11]

opps

[eaugusti, 2012/07/30 20:03:17]

Done.

+
+#include "base/callback.h"
+#include "base/synchronization/lock.h"
+#include "base/memory/ref_counted.h"
+#include "chrome/browser/extensions/extension_service.h"
+
+class GPUFeatureChecker;
+
+namespace extensions {
+class Extension;
+
+// The caller is responsible for maintaining a reference to the
+// RequirementsChecker while it is running.
+class RequirementsChecker {
+ public:
+  RequirementsChecker();
+  ~RequirementsChecker();
+
+  // The vector passed to the callback are any localized errors describing
+  // requirement violations. If this vector is non-empty, requirements checking
+  // failed. This should only be called once from the UI thread. |callback| will
+  // be invoked on |callback_thread|.
+  void Check(scoped_refptr<const Extension> extension,
+      base::Callback<void(std::vector<std::string>)> callback,
+      content::BrowserThread::ID callback_thread);

[Aaron Boodman, 2012/07/30 12:15:11]

Is it possible to just assume that the callback thread is the thread Check() is
called upon?

[eaugusti, 2012/07/30 20:03:17]

Because of GPUFeatureChecker (GPUDataManager), we need make sure that this is
called on the UI thread (see comment for RequirementsChecker::AsWeakPtr()).

[Aaron Boodman, 2012/08/01 03:58:54]

I think that we can require this class to also only be used on the UI thread (it
is common in Chrome for classes to be thread-specific).  Just document it in the
class header: "This class should only be used from the UI thread."

+
+ private:
+  friend class GPUFeatureChecker;
+
+  // Callbacks for the GPUFeatureChecker.
+  void IsWebGLAvailable(bool available);
+  void IsCSS3dAvailable(bool available);

[Aaron Boodman, 2012/07/30 12:15:11]

CSS3D would be more consistent with the other uses of capitalization here.

[eaugusti, 2012/07/30 20:03:17]

Done.

+
+  void MaybeRunCallback();
+  void CallbackOnCorrectThread();
+
+  // These avoid the need for every instance to check with the GPU thread.
+  static bool checked_for_webgl_;

[Aaron Boodman, 2012/07/30 12:15:11]

Is this cache necessary? I thought when I looked at the underlying code that we
call to determine if these things are supported, that it does its own caching.

[eaugusti, 2012/07/30 20:03:17]

You're right.

+  static bool webgl_supported_;
+  static bool checked_for_css3d_;
+  static bool css3d_supported_;
+
+  std::vector<std::string> errors_;
+
+  // Every requirments that needs to be resolved asynchroniously will add to
+  // this counter. When the counter is depleted, the callback will be run.
+  int async_requirement_checks_;
+  base::Lock async_requirement_checks_lock_;

[Aaron Boodman, 2012/07/30 12:15:11]

You should not need this lock. The asynchronous checks are going to call back on
the UI thread, which can only do one thing at a time. Right?

[eaugusti, 2012/07/30 20:03:17]

Done.

+
+  scoped_refptr<GPUFeatureChecker> webgl_checker_;

[Aaron Boodman, 2012/07/30 12:15:11]

These should not need to be refcounted either. The new hotness is WeakPtr. See
base/memory/weak_ptr.h and base/callback.h (the section on weak pointers) for
documentation.

Basically, the callee accepts a base::Callback and just blindly calls it. The
caller passes a Callback wrapping a WeakPtr. The infrastructure makes sure that
the callback is a no-op of the wrapped WeakPtr is invalid.

So, for example, the Callback passed to Check() should be weak (though this
class doesn't care about that detail). And it looks like GPUFeatureChecker also
uses callbacks. In that case, those should be wrapping
WeakPtr<RequirementsChecker>.

[eaugusti, 2012/07/30 20:03:17]

GPUFeatureChecker is already RefCountedThreadSafe (crrev.com/145058), should I
refactor it?

+  scoped_refptr<GPUFeatureChecker> css3d_checker_;
+
+  base::Callback<void(std::vector<std::string>)> callback_;
+  content::BrowserThread::ID callback_thread_;
+};
+
+}  // namespace extensions
+
+#endif  // CHROME_BROWSER_EXTENSIONS_REQUIREMENTS_CHECKER_H_