AW: fix String comparison in shell

No change to production logic, only WebView shell.

This changes a String comparison to use `.equals()` instead of `==`. We
were already returning the same String object, so reference comparison
was probably technically correct as-written, but this change gets rid of
a compile warning from errorprone.

Change-Id: Iaa763f9f48173fd39831a17485ae9ac70dc0cf98
Reviewed-on: https://chromium-review.googlesource.com/745244Reviewed-by: Paul Miller <paulmiller@chromium.org>
Reviewed-by: Bo <boliu@chromium.org>
Commit-Queue: Nate Fischer <ntfschr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#512897}

android_webview/tools/system_webview_shell/apk/src/org/chromium/webview_shell/WebViewBrowserActivity.java

@@ -343,7 +343,7 @@ public class WebViewBrowserActivity extends Activity implements PopupMenu.OnMenu
     @TargetApi(Build.VERSION_CODES.M)
     private boolean canGrant(String webkitPermission) {
         String androidPermission = sPermissions.get(webkitPermission);
-        if (androidPermission == NO_ANDROID_PERMISSION) {
+        if (androidPermission.equals(NO_ANDROID_PERMISSION)) {
             return true;
         }
         return PackageManager.PERMISSION_GRANTED == checkSelfPermission(androidPermission);