Implement state change verifier.

This fixes intermittent waiting bugs in testNewTabHistory by waiting for
all relevant state that we assert to change after page load.
Use isEditingCondition member variables in ToolbarComponent.
Assert state before returning state info in components.
Remove "TODO: Previous..." comments.
Remove outdated todos.
nit: OCD comment updates in testAboutHomeVisibility.
Review comment: Remove space before method call.
Review comment: explicitly set device rotation.
Add ispixel todo.
Add pre-existing StringHelper class.
Review comment: Use StringHelper over defining new urls.
nit: final keyword in UITest.
Review comment: Set private access on View getters.