title: com.google.android.gms.common.SignInButton button not displaying in design using Firebase
body: <p>Connected Firebase with my Android project and here is my <code>build.gradle</code> file code:</p>
  
  <pre><code>apply plugin: 'com.android.application'
  
  android {
      compileSdkVersion 26
      buildToolsVersion "27.0.3"
      defaultConfig {
          applicationId "com.example.seyali_01.firebasegooglein"
          minSdkVersion 23
          targetSdkVersion 26
          versionCode 1
          versionName "1.0"
          testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
      }
      buildTypes {
          release {
              minifyEnabled false
              proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
          }
      }
  }
  
  dependencies {
      compile fileTree(dir: 'libs', include: ['*.jar'])
      androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
          exclude group: 'com.android.support', module: 'support-annotations'
      })
      compile 'com.android.support:appcompat-v7:26.0.0-alpha1'
      testCompile 'junit:junit:4.12'
      compile 'com.google.firebase:firebase-auth:10.2.6'
      compile 'com.google.android.gms:play-services-auth:10.2.6'
      compile 'com.android.support.constraint:constraint-layout:1.0.2'
  }
  
  
  apply plugin: 'com.google.gms.google-services'
  </code></pre>
  
  <p>In my activity_main.xml this is the code</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:tools="http://schemas.android.com/tools"
      android:id="@+id/activity_main"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      tools:context="com.example.seyali_01.firebasegooglein.MainActivity"
      android:background="@drawable/batman"&gt;
  
      &lt;com.google.android.gms.common.SignInButton
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"&gt;
  
      &lt;/com.google.android.gms.common.SignInButton&gt;
  
  &lt;/android.support.constraint.ConstraintLayout&gt;
  </code></pre>
  
  <p>Trying for <code>google-sign-in</code> in my project using Firebase but the default <code>google-signIn</code> button not displaying after adding the above code but it not showing any error in the xml file. Kindly help me to sort out this problem as i'm new to this platform.</p>
  
  <p>I just want to know if the error comes because of <code>ConstraintLayout</code> or mistakes in gradle files kindly help me. Thanks in advance.</p>