Tab Search: Disable dom-repeat chunking after initial render.

Dom-repeat chunking used for the first render of the Tab Search UI
to eliminate the need to render the full list before showing the UI
to the user.

This bounds the time to interactive for users with an arbitrary
number of open tabs.

This CL disables chunking after first load due to flickering when
the tab list updates later on.

Bug: 1099917
Change-Id: I2924756230ef50aea8d0623c0f2a2637623b9b22
Reviewed-on: https://chrome-internal-review.googlesource.com/c/chrome/browser/resources/tab_search/+/3288859Reviewed-by: Yuheng Huang <yuhengh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819615}

chrome/browser/resources/tab_search_merge/app.js

@@ -61,7 +61,6 @@ export class TabSearchAppElement extends PolymerElement {
        */
       chunkingItemCount_: {
         type: Number,
-        readOnly: true,
         value: 10,
       },
 
@@ -161,6 +160,13 @@ export class TabSearchAppElement extends PolymerElement {
               Math.round(window.performance.now()));
           }, 0);
         });
+      } else {
+        // Chunking is used to bound the time to interactive for users
+        // irrespective of the number of tabs they have open. This is no longer
+        // needed after the initial list render and can cause flickering on
+        // updates so disable it here.
+        // TODO(tluk): Investigate a more efficient way to handle this.
+        this.chunkingItemCount_ = 0;
       }
       this.openTabs_ = profileTabs.windows;
     });