md-dialog: first-child margin incorrect

[epelc]

When using md-content inside of md-dialog the margin for every first child element is incorrectly set to 0px.

The styles source can be found here

md-dialog md-content *:first-child {
   margin-top: 0px;
}

This should not be set when using layout="row" other wise you end up with one item being incorrectly positioned. Theres also problems with incorrect spacing when you collapse a row with several columns to one single column.

I think the best solution may be to remove this styling all together. But maybe it could be fixed to apply this styling to the elements layout elements instead.

Some example code to test this with

<md-dialog md-theme="green" aria-label="Settings" flex class="fancy-dialog">
    <md-content>
        <md-subheader class="md-sticky-no-effect" md-theme="blue">My Dialog</md-subheader>
        <p>The first item of ever row ends up with the wrong `margin-top`</p>
        <div layout="row">
            <md-checkbox flex>1</md-checkbox>
            <md-checkbox flex>2</md-checkbox>
            <md-checkbox flex>3</md-checkbox>
        </div>
        <div layout="row">
            <md-checkbox flex>1a</md-checkbox>
            <md-checkbox flex>2a</md-checkbox>
            <md-checkbox flex>3a</md-checkbox>
        </div>
        <div layout="row">
            <md-checkbox flex>1b</md-checkbox>
            <md-checkbox flex>2b</md-checkbox>
            <md-checkbox flex>3b</md-checkbox>
        </div>
        <hr>
        <p>If you use a column or collapse a row to one then you also get incorrect spacing</p>
        <div layout="column">
            <md-checkbox flex>1</md-checkbox>
            <md-checkbox flex>2</md-checkbox>
            <md-checkbox flex>3</md-checkbox>
        </div>
        <div layout="column">
            <md-checkbox flex>1a</md-checkbox>
            <md-checkbox flex>2a</md-checkbox>
            <md-checkbox flex>3a</md-checkbox>
        </div>
        <div layout="column">
            <md-checkbox flex>1b</md-checkbox>
            <md-checkbox flex>2b</md-checkbox>
            <md-checkbox flex>3b</md-checkbox>
        </div>
    </md-content>
    <div class="md-actions" layout="row">
        <md-button ng-click="cancel()" type="button">Cancel</md-button>
        <md-button ng-click="save()" type="submit" class="md-primary">Save</md-button>
    </div>
</md-dialog>