dbus: add support for synchronous PropertySet::Get

dbus/property.h

Index: dbus/property.h
diff --git a/dbus/property.h b/dbus/property.h
index 940ef715d86ba6656a063a99452d1544b58d5668..60aa8e9eb279d7a7a6377c7de7cb7f6bb19b33dc 100644
--- a/dbus/property.h
+++ b/dbus/property.h
@@ -259,6 +259,9 @@ class CHROME_DBUS_EXPORT PropertySet {
   virtual void OnGet(PropertyBase* property, GetCallback callback,
                      Response* response);
 
+  // The synchronous version of Get().

[stevenjb, 2015/09/28 20:24:54]

I assume this is for use outside of Chrome?

I would appreciate a warning that this should never be used on an interactive
thread, e.g. the chrome UI thread. (I realize that should be pretty obvious,
but... once upon a time blocking dbus calls were a huge source of jank on Chrome
OS).

[nywang, 2015/09/28 20:45:33]

Thanks.

Yes this is used outside Chrome. It is for ChromeOS network manager (shill). We
need synchronous get/set to ensure events happen in an expected order.

I will add the warning here.

+  virtual bool GetAndBlock(PropertyBase* property);
+
   // Queries the remote object for values of all properties and updates
   // initial values. Sub-classes may override to use a different D-Bus
   // method, or if the remote object does not support retrieving all
@@ -276,11 +279,12 @@ class CHROME_DBUS_EXPORT PropertySet {
   // depending on the remote object. This method may be overridden by
   // sub-classes if interfaces use different method calls.
   virtual void Set(PropertyBase* property, SetCallback callback);
-  // The sychronous version of Set().
-  virtual bool SetAndBlock(PropertyBase* property);
   virtual void OnSet(PropertyBase* property, SetCallback callback,
                      Response* response);
 
+  // The synchronous version of Set().

[stevenjb, 2015/09/28 20:24:54]

We should add a warning here too.

+  virtual bool SetAndBlock(PropertyBase* property);
+
   // Update properties by reading an array of dictionary entries, each
   // containing a string with the name and a variant with the value, from
   // |message_reader|. Returns false if message is in incorrect format.
@@ -382,6 +386,11 @@ class CHROME_DBUS_EXPORT Property : public PropertyBase {
     property_set()->Get(this, callback);
   }
 
+  // The synchronous version of Get().
+  virtual bool GetAndBlock() {
+    return property_set()->GetAndBlock(this);
+  }
+
   // Requests that the remote object change the property value to |value|,
   // |callback| will be called to indicate the success or failure of the
   // request, however the new value may not be available depending on the
@@ -391,7 +400,7 @@ class CHROME_DBUS_EXPORT Property : public PropertyBase {
     property_set()->Set(this, callback);
   }
 
-  // The sychronous version of Set().
+  // The synchronous version of Set().
   virtual bool SetAndBlock(const T& value) {
     set_value_ = value;
     return property_set()->SetAndBlock(this);