Fix blank card issue in Grid Tab Switcher

In getTabThumbnailWithCallback() with forceUpdate == true,
cacheTabThumbnail() should be called after the callback of
nativeGetTabThumbnailWithCallback(). Otherwise there is no guarantee
the callback of cacheTabThumbnail() would be run after the callback
of nativeGetTabThumbnailWithCallback().

Bug: 965891
Change-Id: Ia8cf42f4942d569e4b646820063460a297160d9f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1629808Reviewed-by: Matthew Jones <mdjones@chromium.org>
Commit-Queue: Wei-Yin Chen (陳威尹) <wychen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#664364}

chrome/android/java/src/org/chromium/chrome/browser/compositor/layouts/content/TabContentManager.java

@@ -263,11 +263,15 @@ public class TabContentManager {
             Tab tab, Callback<Bitmap> callback, boolean forceUpdate) {
         if (mNativeTabContentManager == 0 || !mSnapshotsEnabled) return;
 
+        if (!forceUpdate) {
+            nativeGetTabThumbnailWithCallback(mNativeTabContentManager, tab.getId(), callback);
+            return;
+        }
+
         // Reading thumbnail from disk is faster than taking screenshot from live Tab, so fetch
         // that first even if |forceUpdate|.
-        nativeGetTabThumbnailWithCallback(mNativeTabContentManager, tab.getId(), callback);
-
-        if (forceUpdate) {
+        nativeGetTabThumbnailWithCallback(mNativeTabContentManager, tab.getId(), (diskBitmap) -> {
+            callback.onResult(diskBitmap);
             cacheTabThumbnail(tab, (bitmap) -> {
                 // Null check to avoid having a Bitmap from nativeGetTabThumbnailWithCallback() but
                 // cleared here.
@@ -277,7 +281,7 @@ public class TabContentManager {
                     callback.onResult(bitmap);
                 }
             });
-        }
+        });
     }
 
     /**