Embedding Projector: update tsne learning rate during iteration (#6319)

## Motivation for features / changes
#6289

## Technical description of changes
new tsne learning rate will take effect during next tsne iteration

## Screenshots of UI changes
N/A

## Detailed steps to verify changes work correctly (as executed by you)
1. Open t-SNE projection
1. Adjust learning rate
1. Verify a small learning rate will stall changes and a large learning
rate will accelerate changes between iterations

## Alternate designs / implementations considered

Author: alicialics

tensorboard/plugins/projector/vz_projector/bh_tsne.ts

@@ -259,7 +259,7 @@ export class TSNE {
   constructor(opt: TSNEOptions) {
     opt = opt || {dim: 2};
     this.perplexity = opt.perplexity || 30;
-    this.epsilon = opt.epsilon || 10;
+    this.setEpsilon(opt.epsilon || 10);
     this.rng = opt.rng || Math.random;
     this.dim = opt.dim;
     if (opt.dim === 2) {
@@ -383,6 +383,9 @@ export class TSNE {
       }
     }
   }
+  setEpsilon(epsilon: number) {
+    this.epsilon = epsilon;
+  }
   setSupervision(superviseLabels: string[], superviseInput?: string) {
     if (superviseLabels != null) {
       this.labels = superviseLabels;

tensorboard/plugins/projector/vz_projector/data.ts

@@ -503,6 +503,11 @@ export class DataSet {
       });
     }
   }
+  setTsneLearningRate(learningRate: number) {
+    if (this.tsne) {
+      this.tsne.setEpsilon(learningRate);
+    }
+  }
   setSupervision(superviseColumn: string, superviseInput?: string) {
     if (superviseColumn != null) {
       this.superviseLabels = this.shuffledDataIndices

tensorboard/plugins/projector/vz_projector/vz-projector-projections-panel.ts

@@ -161,6 +161,9 @@ class ProjectionsPanel extends LegacyElementMixin(PolymerElement) {
   private updateTSNELearningRateFromUIChange() {
     if (this.learningRateInput) {
       this.learningRate = Math.pow(10, +this.learningRateInput.value);
+      if (this.dataSet) {
+        this.dataSet.setTsneLearningRate(this.learningRate);
+      }
     }
     (this.$$('.tsne-learning-rate span') as HTMLSpanElement).innerText =
       '' + this.learningRate;