Added handling of network ("service" in flimflam parlance) property changes. 
NetworkLibrary updates its Network objects in response to property changes, 
then calls any NetworkObservers that have registered for the given network. 

Use the is_active member of Network in various places to ensure that we are 
dealing with the correct network. 

Created separate observer classes for NetworkManager, Network, and 
CellularDataPlan, so that monitors can be established independently for each 
of them. Changed the callback method names to prepend "On", i.e., 
OnNetworkManagerChanged, OnNetworkChanged, OnCellularDataPlanChanged. 

Wired up signal strength update and network technology update in the status 
bar, network dropdown menu, and internet settings page. 

Added new icon badges for 1xRTT radio technology. These are used when EVDO 
coverage switches to 1xRTT. Just as is the case for the 3G icons, there are 
three 1x icons: normal, warn, and error. Please consider these icons to be 
placeholders if the UI folks think they need to be redesigned. 

Centralized choosing of the network technology badge in 
NetworkMenu::BadgeForNetworkTechnology. 

BUG=chromium-os:5612:chromium-os:7619,chromium-os:5917,chromium-os:4674 
TEST=Extensive manual testing with different combinations of wi-fi and 
cellular networks connected and disconnected. Used a modified version 
of flimflam that randomly changes reported signal strength, network 
technology, and roaming state, and verified that the UI correctly reflected 
current values for the active network (roaming is not handled in the UI 
at this time).
Review URL: http://codereview.chromium.org/4235005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@64888 0039d316-1c4b-4281-b951-d872f2087c98