Make pause-on-exceptions toggle/tri-state button.

Source/devtools/front_end/DebuggerModel.js

Index: Source/devtools/front_end/DebuggerModel.js
diff --git a/Source/devtools/front_end/DebuggerModel.js b/Source/devtools/front_end/DebuggerModel.js
index b342c752b73c8a30d4cf8521145242f6b60bae80..7fa4b4908d7815cba3806f8e3b222f94924b8be3 100644
--- a/Source/devtools/front_end/DebuggerModel.js
+++ b/Source/devtools/front_end/DebuggerModel.js
@@ -49,6 +49,8 @@ WebInspector.DebuggerModel = function()
     WebInspector.settings.pauseOnExceptionStateString = WebInspector.settings.createSetting("pauseOnExceptionStateString", WebInspector.DebuggerModel.PauseOnExceptionsState.DontPauseOnExceptions);
     WebInspector.settings.pauseOnExceptionStateString.addChangeListener(this._pauseOnExceptionStateChanged, this);
 
+    WebInspector.settings.lastPauseOnExceptionState = WebInspector.settings.createSetting("lastPauseOnExceptionState", WebInspector.DebuggerModel.PauseOnExceptionsState.PauseOnUncaughtExceptions);
+
     WebInspector.settings.enableAsyncStackTraces.addChangeListener(this._asyncStackTracesStateChanged, this);
 
     this.enableDebugger();
@@ -56,7 +58,11 @@ WebInspector.DebuggerModel = function()
     WebInspector.DebuggerModel.applySkipStackFrameSettings();
 }
 
-// Keep these in sync with WebCore::ScriptDebugServer
+/**
+ * Keep these in sync with WebCore::ScriptDebugServer
+ *
+ * @enum {string}
+ */
 WebInspector.DebuggerModel.PauseOnExceptionsState = {
     DontPauseOnExceptions : "none",
     PauseOnAllExceptions : "all",