Bug 224971

Asserting that function or variable is accessed in a certain thread should be simpler and more robust Currently thread assertions are of form: ASSERT(isMainThread()); ASSERT(!isMainThread()); These are sometimes applied and sometimes not. Especially the latter is quite vague. This creates small consistency problems. For example, WeakPtr has the property that it must be dereferenced in the thread that owns the WeakPtrFactory. However, the assertion is only done for main thread. It would be beneficial to have following additions: 1) Possibility to assert arbitrary thread 2) Possibility to enforce the thread access compile-time through thread safety analysis.