Add an extension bubble explaining which extensions are in dev mode.

extensions/common/extension.h

Index: extensions/common/extension.h
diff --git a/extensions/common/extension.h b/extensions/common/extension.h
index 4da7a03625e7c02d4f2093254aaf007fb9e49afd..db1e31cdc08063a7c216ae4b7594843641a11f05 100644
--- a/extensions/common/extension.h
+++ b/extensions/common/extension.h
@@ -259,6 +259,9 @@ class Extension : public base::RefCountedThreadSafe<Extension> {
   // includes non-component apps that are hidden from the app launcher and ntp.
   bool ShouldNotBeVisible() const;
 
+  // Returns true if the extension is considered a Developer Mode extension.
+  bool IsDevModeExtension() const;

[not at google - send to devlin, 2013/12/04 17:25:13]

I think this belongs in extension_util.h if anywhere. I'm not sure that the
model should care about this though, it's an interpretation of the data that
this is loaded in "developer mode". Could it go in one of the controller classes
instead?

[Finnur, 2013/12/05 23:55:56]

Sure. Done.

+
   // Get the manifest data associated with the key, or NULL if there is none.
   // Can only be called after InitValue is finished.
   ManifestData* GetManifestData(const std::string& key) const;