[Android] Cache document-mode command-line check

FeatureUtilities.isDocumentMode can be called relatively frequently.
Avoid the cost of the associated JNI command-line call and string
conversion by caching the result of the "--disable-document-mode"
query.

BUG=457748

Review URL: https://codereview.chromium.org/1255733002

Cr-Commit-Position: refs/heads/master@{#340185}

chrome/android/java/src/org/chromium/chrome/browser/util/FeatureUtilities.java

@@ -32,6 +32,7 @@
 public class FeatureUtilities {
     private static Boolean sHasGoogleAccountAuthenticator;
     private static Boolean sHasRecognitionIntentHandler;
+    private static Boolean sDocumentModeDisabled;
 
     /**
      * Determines whether or not the {@link RecognizerIntent#ACTION_WEB_SEARCH} {@link Intent}
@@ -95,11 +96,13 @@ private static boolean hasSyncPermissions(Context context) {
      * @return Whether Chrome should be running on document mode.
      */
     public static boolean isDocumentMode(Context context) {
+        if (sDocumentModeDisabled == null && CommandLine.getInstance() != null) {
+            sDocumentModeDisabled = CommandLine.getInstance().hasSwitch(
+                    ChromeSwitches.DISABLE_DOCUMENT_MODE);
+        }
         return isDocumentModeEligible(context)
                 && !DocumentModeManager.getInstance(context).isOptedOutOfDocumentMode()
-                && ((CommandLine.getInstance() == null)
-                    || !CommandLine.getInstance().hasSwitch(
-                            ChromeSwitches.DISABLE_DOCUMENT_MODE));
+                && (sDocumentModeDisabled == null || !sDocumentModeDisabled.booleanValue());
     }
 
     /**