Sanitize PrefStore interface.

This reworks the PrefStore interface, specifically:

- Split up the interface into PrefStore, which only provides reading functionality, and the derived PersistentPrefStore for the actual user pref store
- Remove the hurt-me-plenty prefs() function from PrefStore, instead provide Get/Set/Remove operations
- Remove special handling of default and user pref store from PrefValueStore and put it into PrefService
- Pref change notification handling now almost exclusively handled through PrefValueStore
- Adjust all consumers of these interfaces (but keep ConfigurationPolicyPrefStore untouched, that's up next on the list)

BUG=64232
TEST=existing unit tests

Review URL: http://codereview.chromium.org/5646003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@68736 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 17 insertions, 49 deletions

diff --git a/chrome/common/pref_store.h b/chrome/common/pref_store.h
index 808ffbd2..745eff7 100644
--- a/chrome/common/pref_store.h
+++ b/chrome/common/pref_store.h
@@ -10,7 +10,6 @@
 
 #include "base/basictypes.h"
 
-class DictionaryValue;
 class Value;
 
 // This is an abstract interface for reading and writing from/to a persistent
@@ -23,9 +22,9 @@ class Value;
 class PrefStore {
  public:
   // Observer interface for monitoring PrefStore.
-  class ObserverInterface {
+  class Observer {
    public:
-    virtual ~ObserverInterface() {}
+    virtual ~Observer() {}
 
     // Called when the value for the given |key| in the store changes.
     virtual void OnPrefValueChanged(const std::string& key) = 0;
@@ -33,61 +32,30 @@ class PrefStore {
     virtual void OnInitializationCompleted() = 0;
   };
 
-  // Unique integer code for each type of error so we can report them
-  // distinctly in a histogram.
-  // NOTE: Don't change the order here as it will change the server's meaning
-  // of the histogram.
-  enum PrefReadError {
-    PREF_READ_ERROR_NONE = 0,
-    PREF_READ_ERROR_JSON_PARSE,
-    PREF_READ_ERROR_JSON_TYPE,
-    PREF_READ_ERROR_ACCESS_DENIED,
-    PREF_READ_ERROR_FILE_OTHER,
-    PREF_READ_ERROR_FILE_LOCKED,
-    PREF_READ_ERROR_NO_FILE,
-    PREF_READ_ERROR_JSON_REPEAT,
-    PREF_READ_ERROR_OTHER,
-    PREF_READ_ERROR_FILE_NOT_SPECIFIED
+  // Return values for GetValue().
+  enum ReadResult {
+    // Value found and returned.
+    READ_OK,
+    // No value present, but skip other pref stores and use default.
+    READ_USE_DEFAULT,
+    // No value present.
+    READ_NO_VALUE,
   };
 
-  // To require that the default value be used for a preference, a
-  // PrefStore can set the value in its own prefs dictionary to the
-  // sentinel Value returned by this function.
-  // TODO(danno): Instead of having a sentinel value, pref stores
-  // should return a richer set of information from the property
-  // accessor methods to indicate that the default should be used.
-  static Value* CreateUseDefaultSentinelValue();
-
-  // Returns true if a value is the special sentinel value created by
-  // CreateUseDefaultSentinelValue.
-  static bool IsUseDefaultSentinelValue(Value* value);
-
   PrefStore() {}
   virtual ~PrefStore() {}
 
   // Add and remove observers.
-  virtual void AddObserver(ObserverInterface* observer) {}
-  virtual void RemoveObserver(ObserverInterface* observer) {}
+  virtual void AddObserver(Observer* observer) {}
+  virtual void RemoveObserver(Observer* observer) {}
 
   // Whether the store has completed all asynchronous initialization.
-  virtual bool IsInitializationComplete() { return true; }
-
-  // Whether the store is in a pseudo-read-only mode where changes are not
-  // actually persisted to disk.  This happens in some cases when there are
-  // read errors during startup.
-  virtual bool ReadOnly() const { return true; }
-
-  // TODO(danno): PrefValueStore shouldn't allow direct access to the
-  // DictionaryValue. Instead, it should have getters that return a
-  // richer set of information for a pref, including if the store
-  // wants to return the default value for a preference.
-  virtual DictionaryValue* prefs() const = 0;
-
-  virtual PrefReadError ReadPrefs() = 0;
-
-  virtual bool WritePrefs() { return true; }
+  virtual bool IsInitializationComplete() const { return true; }
 
-  virtual void ScheduleWritePrefs() { }
+  // Get the value for a given preference |key| and stores it in |result|.
+  // |result| is only modified if the return value is READ_OK. Ownership of the
+  // |result| value remains with the PrefStore.
+  virtual ReadResult GetValue(const std::string& key, Value** result) const = 0;
 
   DISALLOW_COPY_AND_ASSIGN(PrefStore);
 };