DevTools: the sources debug toolbar buttons should not be drag targets

BUG=728789

Review-Url: https://codereview.chromium.org/2915013003
Cr-Commit-Position: refs/heads/master@{#476500}

third_party/WebKit/Source/devtools/front_end/sources/SourcesPanel.js

@@ -1056,7 +1056,7 @@ Sources.SourcesPanel = class extends UI.Panel {
       this._sidebarPaneStack.showView(jsBreakpoints);
       this._extensionSidebarPanesContainer = this._sidebarPaneStack;
       this.sidebarPaneView = vbox;
-      this._splitWidget.uninstallResizer(this._debugToolbar.element);
+      this._splitWidget.uninstallResizer(this._debugToolbar.gripElementForResize());
     } else {
       var splitWidget = new UI.SplitWidget(true, true, 'sourcesPanelDebuggerSidebarSplitViewState', 0.5);
       splitWidget.setMainWidget(vbox);
@@ -1068,7 +1068,7 @@ Sources.SourcesPanel = class extends UI.Panel {
       splitWidget.setSidebarWidget(tabbedLocation.tabbedPane());
       this._tabbedLocationHeader = tabbedLocation.tabbedPane().headerElement();
       this._splitWidget.installResizer(this._tabbedLocationHeader);
-      this._splitWidget.installResizer(this._debugToolbar.element);
+      this._splitWidget.installResizer(this._debugToolbar.gripElementForResize());
       tabbedLocation.appendView(scopeChainView);
       tabbedLocation.appendView(this._watchSidebarPane);
       this._extensionSidebarPanesContainer = tabbedLocation;

third_party/WebKit/Source/devtools/front_end/ui/Toolbar.js

@@ -193,6 +193,13 @@ UI.Toolbar = class {
     return UI.Toolbar.createActionButton(/** @type {!UI.Action} */ (action));
   }
 
+  /**
+   * @return {!Element}
+   */
+  gripElementForResize() {
+    return this._contentElement;
+  }
+
   /**
    * @param {boolean=} reverse
    * @param {boolean=} growVertically