docs(table): incorrect initial request in http example (#14692)

Fixes the first request in the table HTTP example being incorrect due to some of the data not being initialized. Also cleans up the example a bit.

Fixes #14683.

Author: crisbeto

src/material-examples/table-http/table-http-example.css

@@ -1,6 +1,7 @@
 /* Structure */
 .example-container {
   position: relative;
+  min-height: 200px;
 }
 
 .example-table-container {

src/material-examples/table-http/table-http-example.html

@@ -10,7 +10,7 @@
   <div class="example-table-container">
 
     <table mat-table [dataSource]="data" class="example-table"
-           matSort matSortActive="created" matSortDisableClear matSortDirection="asc">
+           matSort matSortActive="created" matSortDisableClear matSortDirection="desc">
       <!-- Number Column -->
       <ng-container matColumnDef="number">
         <th mat-header-cell *matHeaderCellDef>#</th>

src/material-examples/table-http/table-http-example.ts

@@ -1,5 +1,5 @@
 import {HttpClient} from '@angular/common/http';
-import {Component, OnInit, ViewChild} from '@angular/core';
+import {Component, ViewChild, AfterViewInit} from '@angular/core';
 import {MatPaginator, MatSort} from '@angular/material';
 import {merge, Observable, of as observableOf} from 'rxjs';
 import {catchError, map, startWith, switchMap} from 'rxjs/operators';
@@ -12,9 +12,9 @@ import {catchError, map, startWith, switchMap} from 'rxjs/operators';
   styleUrls: ['table-http-example.css'],
   templateUrl: 'table-http-example.html',
 })
-export class TableHttpExample implements OnInit {
+export class TableHttpExample implements AfterViewInit {
   displayedColumns: string[] = ['created', 'state', 'number', 'title'];
-  exampleDatabase: ExampleHttpDao | null;
+  exampleDatabase: ExampleHttpDatabase | null;
   data: GithubIssue[] = [];
 
   resultsLength = 0;
@@ -26,8 +26,8 @@ export class TableHttpExample implements OnInit {
 
   constructor(private http: HttpClient) {}
 
-  ngOnInit() {
-    this.exampleDatabase = new ExampleHttpDao(this.http);
+  ngAfterViewInit() {
+    this.exampleDatabase = new ExampleHttpDatabase(this.http);
 
     // If the user changes the sort order, reset back to the first page.
     this.sort.sortChange.subscribe(() => this.paginator.pageIndex = 0);
@@ -71,7 +71,7 @@ export interface GithubIssue {
 }
 
 /** An example database that the data source uses to retrieve data for the table. */
-export class ExampleHttpDao {
+export class ExampleHttpDatabase {
   constructor(private http: HttpClient) {}
 
   getRepoIssues(sort: string, order: string, page: number): Observable<GithubApi> {