Apply the light theme for PerfTestActivity

This CL restores the window background color back to white. The IME
color is  light as well. So when the IME is showing and hiding, the
gesture navigation bar won't need to change its color to adapt the
background, which might consume additional CPU resource.

Fix: 334024581
Flag: NA
Test: ImePerfTest#testShowImeWarm
Change-Id: I83bf308933d63cb138353d682a66cb8f6e1eb07a
diff --git a/apct-tests/perftests/inputmethod/AndroidManifest.xml b/apct-tests/perftests/inputmethod/AndroidManifest.xml
index 5dd6ccc..34f9692 100644
--- a/apct-tests/perftests/inputmethod/AndroidManifest.xml
+++ b/apct-tests/perftests/inputmethod/AndroidManifest.xml
@@ -22,7 +22,7 @@
     <application>
         <uses-library android:name="android.test.runner" />
         <activity android:name="android.perftests.utils.PerfTestActivity"
-                  android:theme="@android:style/Theme.DeviceDefault.NoActionBar"
+                  android:theme="@android:style/Theme.DeviceDefault.Light.NoActionBar"
                   android:exported="true">
           <intent-filter>
             <action android:name="com.android.perftests.core.PERFTEST" />