Polymer: disable data binding on style attribute

For security enhanced TensorBoard, we use polymer-resin. It fails to correctly sanitize data-bound style attribute and completely omits the style.

Very simple regex found few 7 instances of the violations:

tensorboard/plugins/text/tf_text_dashboard/tf-text-loader.html
39:      style="border-color: [[_runColor]]"

tensorboard/plugins/graph/tf_graph_debugger_data_card/tf-graph-debugger-data-card.html
246:            style="background:[[item.background_color]]"

tensorboard/plugins/graph/tf_graph_controls/tf-graph-controls.html
600:                    style="fill:[[item.color]]"

tensorboard/plugins/pr_curve/tf_pr_curve_dashboard/tf-pr-curve-steps-selector.html
31:            style="background:[[_computeColorForRun(run)]];"

tensorboard/plugins/pr_curve/tf_pr_curve_dashboard/tf-pr-curve-card.html
75:            style="background: [[_computeRunColor(run)]];"

tensorboard/plugins/projector/vz_projector/vz-projector-legend.html
57:        <div class="shape" style="background-color: [[item.color]];"></div>
59:        <div class="info" style="color: [[item.color]];">[[item.count]]</div>

Start with the seven HTML templates and the listed style bindings, then check how polymer-resin handles data-bound style attributes. Verify the affected dashboards and confirm that the intended colors and borders still render without triggering the sanitizer issue.