Steps:

1) Open the Profiler window
2) Make sure you're in "Timeline" display mode
3) Click on "Profiler Editor"

Observe the error in console window.

Expected result: no error is thrown
Actual result: following error is thrown

Reproducible on :2018.2.0b1, 2018.2.0a8, 2018.2.0a7, 2018.2.0a5

Working fine on:2018.2.0a4, 2018.2.0a1, 2018.1.0b13.

Environment:
Occurring on Windows 10, Windows 7, Mac 10.13.

Error Details:
NullReferenceException: Object reference not set to an instance of an object
UnityEditor.ProfilerWindow.DrawMainToolbar () (at C:/buildslave/unity/build/Modules/ProfilerEditor/ProfilerWindow/ProfilerWindow.cs:1303)
UnityEditor.ProfilerWindow.OnGUI () (at C:/buildslave/unity/build/Modules/ProfilerEditor/ProfilerWindow/ProfilerWindow.cs:1473)
System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MonoMethod.cs:222)
Rethrow as TargetInvocationException: Exception has been thrown by the target of an invocation.
System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MonoMethod.cs:232)
System.Reflection.MethodBase.Invoke (System.Object obj, System.Object[] parameters) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MethodBase.cs:115)
UnityEditor.HostView.Invoke (System.String methodName, System.Object obj) (at C:/buildslave/unity/build/Editor/Mono/HostView.cs:295)
UnityEditor.HostView.Invoke (System.String methodName) (at C:/buildslave/unity/build/Editor/Mono/HostView.cs:288)
UnityEditor.HostView.InvokeOnGUI (Rect onGUIPosition) (at C:/buildslave/unity/build/Editor/Mono/HostView.cs:255)

NOTE: if you stop profiling, switch to another mode, then switch back to "Timeline" mode, the error is not thrown anymore (as seen in the gif below).

Repro on latest trunk 1ea6a37d6fce