Checking `textContent` means that components that have dynamic content or content in shadow DOM fail

[KeithHenry]

The show action checks that content is populated before displaying it, and it does this by checking for textContent:

paper-tooltip/paper-tooltip.js

Lines 385 to 398 in 67a2272

	if (dom(this).textContent.trim() === '') {
	// Check if effective children are also empty
	var allChildrenEmpty = true;
	var effectiveChildren = dom(this).getEffectiveChildNodes();
	for (var i = 0; i < effectiveChildren.length; i++) {
	if (effectiveChildren[i].textContent.trim() !== '') {
	allChildrenEmpty = false;
	break;
	}
	}
	if (allChildrenEmpty) {
	return;
	}
	}

The problem is if you have something like:

<paper-tooltip>
    <my-component></my-component>
</paper-tooltip>

Now <my-component> might have a textContent, but if it doesn't the tooltip never shows.