Make CardViewActivity in Support7Demos extend AppCompatActivity.

Activities that use AppCompat themes must extend AppCompatActivity.

Bug: 27453786
Change-Id: I9c780fd17ee0a98ec0579b43dba754ea5d525d10
diff --git a/samples/Support7Demos/AndroidManifest.xml b/samples/Support7Demos/AndroidManifest.xml
index 7d9c242..a75879e 100644
--- a/samples/Support7Demos/AndroidManifest.xml
+++ b/samples/Support7Demos/AndroidManifest.xml
@@ -436,7 +436,7 @@
 
         <activity android:name=".view.CardViewActivity"
                   android:label="@string/card_view"
-                  android:theme="@style/Theme.AppCompat">
+                  android:theme="@style/Theme.AppCompat.Light.NoActionBar">
             <intent-filter>
                 <action android:name="android.intent.action.MAIN" />
                 <category android:name="com.example.android.supportv7.SAMPLE_CODE" />
diff --git a/samples/Support7Demos/src/com/example/android/supportv7/view/CardViewActivity.java b/samples/Support7Demos/src/com/example/android/supportv7/view/CardViewActivity.java
index f5f8c4c..e047186 100644
--- a/samples/Support7Demos/src/com/example/android/supportv7/view/CardViewActivity.java
+++ b/samples/Support7Demos/src/com/example/android/supportv7/view/CardViewActivity.java
@@ -15,10 +15,10 @@
  */
 package com.example.android.supportv7.view;
 
-import android.app.Activity;
 import android.os.Bundle;
 import android.os.Handler;
 import android.support.v4.view.ViewCompat;
+import android.support.v7.app.AppCompatActivity;
 import android.support.v7.widget.CardView;
 import android.view.View;
 import android.view.ViewGroup;
@@ -28,7 +28,7 @@
 
 import com.example.android.supportv7.R;
 
-public class CardViewActivity extends Activity {
+public class CardViewActivity extends AppCompatActivity {
 
     CardView mCardView;