fix missing TypeScript code

static/js/services/build/build.service.ts

@@ -0,0 +1,19 @@
+/**
+ * Service which provides helper methods for reasoning about builds.
+ */
+export abstract class BuildService {
+
+  /**
+   * Determine if the given build is active.
+   * @param build The build object.
+   * @return isActive If the given build is active.
+   */
+  public abstract isActive(build: {phase: string}): boolean;
+
+  /**
+   * Generate a message based on a given phase.
+   * @param phase The phase type.
+   * @return buildMessage The message associated with the given phase.
+   */
+  public abstract getBuildMessage(phase: string): string;
+}