Put WebAPK Android Manifest keys in dedicated file

chrome/android/webapk/shell_apk/src/org/chromium/webapk/shell_apk/MainActivity.java

Index: chrome/android/webapk/shell_apk/src/org/chromium/webapk/shell_apk/MainActivity.java
diff --git a/chrome/android/webapk/shell_apk/src/org/chromium/webapk/shell_apk/MainActivity.java b/chrome/android/webapk/shell_apk/src/org/chromium/webapk/shell_apk/MainActivity.java
index d3ae07b4e0399bfe2374f37daa8b8573fef4e3c4..ecc89d205a86e1c7ea2e88e2106d3fa603377e37 100644
--- a/chrome/android/webapk/shell_apk/src/org/chromium/webapk/shell_apk/MainActivity.java
+++ b/chrome/android/webapk/shell_apk/src/org/chromium/webapk/shell_apk/MainActivity.java
@@ -16,6 +16,7 @@ import android.os.Bundle;
 import android.util.Log;
 
 import org.chromium.webapk.lib.common.WebApkConstants;
+import org.chromium.webapk.lib.common.WebApkMetaDataKeys;
 
 import java.lang.reflect.Method;
 import java.net.URISyntaxException;
@@ -37,9 +38,6 @@ public class MainActivity extends Activity {
     private static final String REUSE_URL_MATCHING_TAB_ELSE_NEW_TAB =
             "REUSE_URL_MATCHING_TAB_ELSE_NEW_TAB";
 
-    // Key for start URL in Android Manifest.
-    private static final String META_DATA_START_URL = "org.chromium.webapk.shell_apk.startUrl";
-
     /**
      * Key for passing app icon id.
      */
@@ -171,6 +169,6 @@ public class MainActivity extends Activity {
         } catch (NameNotFoundException e) {
             return null;
         }
-        return appInfo.metaData.getString(META_DATA_START_URL);
+        return appInfo.metaData.getString(WebApkMetaDataKeys.START_URL);
     }
 }