[DevTools] Make log agent optional.

Non-browser targets (e.g. Node.js) do not have log domain.

BUG=

Review-Url: https://codereview.chromium.org/2297803002
Cr-Commit-Position: refs/heads/master@{#415450}

third_party/WebKit/Source/devtools/front_end/sdk/ConsoleModel.js

@@ -32,8 +32,9 @@
  * @constructor
  * @extends {WebInspector.SDKModel}
  * @param {!WebInspector.Target} target
+ * @param {?Protocol.LogAgent} logAgent
  */
-WebInspector.ConsoleModel = function(target)
+WebInspector.ConsoleModel = function(target, logAgent)
 {
     WebInspector.SDKModel.call(this, WebInspector.ConsoleModel, target);
 
@@ -44,9 +45,9 @@ WebInspector.ConsoleModel = function(target)
     this._warnings = 0;
     this._errors = 0;
     this._revokedErrors = 0;
-    this._logAgent = target.logAgent();
     target.registerLogDispatcher(new WebInspector.LogDispatcher(this));
-    this._logAgent.enable();
+    this._logAgent = logAgent;
+    this._logAgent && this._logAgent.enable();
 }
 
 /** @enum {symbol} */
@@ -134,7 +135,7 @@ WebInspector.ConsoleModel.prototype = {
 
     requestClearMessages: function()
     {
-        this._logAgent.clear();
+        this._logAgent && this._logAgent.clear();
         this.clear();
     },
 

third_party/WebKit/Source/devtools/front_end/sdk/TargetManager.js

@@ -190,8 +190,10 @@ WebInspector.TargetManager.prototype = {
     {
         var target = new WebInspector.Target(this, name, capabilitiesMask, connection, parentTarget);
 
+        var logAgent = target.hasBrowserCapability() ? target.logAgent() : null;
+
         /** @type {!WebInspector.ConsoleModel} */
-        target.consoleModel = new WebInspector.ConsoleModel(target);
+        target.consoleModel = new WebInspector.ConsoleModel(target, logAgent);
         /** @type {!WebInspector.RuntimeModel} */
         target.runtimeModel = new WebInspector.RuntimeModel(target);