[Instant Start] Gate prepareToShowStartPagePreNative by Start flag.

Add a Start surface check for
ChromeTabbedActivity#prepareToShowStartPagePreNative.

Bug: 1139055, 1140406
Change-Id: I351359fde6af17af4f9fbac05ea50f8a8bdd774c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2528623Reviewed-by: Yaron Friedman <yfriedman@chromium.org>
Reviewed-by: Xi Han <hanxi@chromium.org>
Reviewed-by: Wei-Yin Chen (陳威尹) <wychen@chromium.org>
Commit-Queue: Hao Dong <spdonghao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#826575}

chrome/android/java/src/org/chromium/chrome/browser/ChromeTabbedActivity.java

@@ -1567,7 +1567,8 @@ public class ChromeTabbedActivity extends ChromeActivity<ChromeActivityComponent
         // tablet), a view-only start page created on Java will be shown before native is
         // initialized. The {@link prepareToShowStartPagePreNative()} is only called in a cold
         // start.
-        if (TabUiFeatureUtilities.supportInstantStart(isTablet()) && !hadWarmStart()) {
+        if (StartSurfaceConfiguration.isStartSurfaceEnabled()
+                && TabUiFeatureUtilities.supportInstantStart(isTablet()) && !hadWarmStart()) {
             prepareToShowStartPagePreNative();
         }
     }