feat(datadog): add type tag

Always add a tag for the type of asset. Examples:
* type:js
* type:css

README.md

@@ -53,5 +53,7 @@ new DataDogStatsReporter(options: DataDogStatsReporterOptions);
 - `apiKey: string`: Your DataDog API key
 - `gzipSize?: boolean = true`: Report gzipped size if true, uncompressed size if false
 - `metricName: string`: The base name for the metric
-- `tags?: string[]`: Custom tags for the metric. A `chunk` tag is always added.
+- `tags?: string[]`: Custom tags for the metric. The following tags are always added:
+  * `chunk`: the chunk name
+  * `type`: the type of asset (js, css, etc)
 - `test?: RegExp`: Test to match files against. If not set, stats for all emitted assets will be sent.

src/reporters/datadog.ts

@@ -52,7 +52,7 @@ export class DataDogStatsReporter implements StatsReporter {
     }
   }
 
-  private filterAssets(stats: any) {
+  private filterAssets(stats: any): string[] {
     const { assets } = stats;
     if (!this.test) {
       return assets;
@@ -72,14 +72,18 @@ export class DataDogStatsReporter implements StatsReporter {
       return {
         metric: `${this.metricName}.bytes${path.extname(asset.name)}`,
         points: [[now, size]],
-        tags: [...this.tags, `chunk:${asset.chunkNames[0]}`],
+        tags: [
+          ...this.tags,
+          `chunk:${asset.chunkNames[0]}`,
+          `type:${path.extname(asset.name).substring(1)}`
+        ],
         type: METRIC_TYPE_GAUGE
       };
     });
     return Promise.all(promises);
   }
 
-  private validateOptions() {
+  private validateOptions(): void {
     const errors = [];
     if (!this.apiKey) {
       errors.push('apiKey is required.');