[Query Tiles]: Add README.md

Change-Id: If317deecc81f259bcf6bf6c44c10a65cf3f1ddac
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2271015Reviewed-by: Shakti Sahu <shaktisahu@chromium.org>
Commit-Queue: Hesen Zhang <hesen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#783844}

components/query_tiles/README.md

+# Query Tiles Service
+
+## Introduction
+Query tiles is a new feature to bring down the barriers for NIU users and boost
+their confidence when using Chrome in Android.  It encourages users to explore
+the internet by simply clicking on a few image tiles, and building a search
+query to find the information they want.
+
+With this feature enabled, users will see a list of image tiles with the
+corresponding query strings shown on NTP(new tab page) and Omnibox suggestions.
+By clicking on those tiles, users will be directed to the search result page
+provided.
+
+The client side will schedule fetch tasks from Google server periodically to
+update the latest data and images based on the user's locale.
+
+## Code structure
+
+[components/query_tiles](.)
+Public interfaces and data structure.
+
+[components/query_tiles/internal](./internal)
+internal implementations.
+
+[components/query_tiles/proto](./proto)
+Protobuf structure.
+
+[components/query_tiles/android](./android)
+UI related code.
+
+[chrome/browser/query_tiles](../../chrome/browser/query_tiles)
+include service factory and background task client code.
+
+[components/browser_ui/widget/image_tiles](../browser_ui/widget/android/java/src/org/chromium/components/browser_ui/widget/image_tiles/)
+Generic widget representing image tiles carousel.
+
+`TileService` - Public interface for query tile service.
+
+`TileServiceScheduer` - Handles scheduling tasks to fetch tiles from the server.
+
+`TileManager` - Store and dispense query tiles.
+
+`ImageTileCoordinator` - UI widget representing the carousel.
+
+`TileProvider` - Handles backend interaction from the Java layer
+
+`QueryTileSection` - Query tiles widget on NTP.
+
+`QueryTileProvider` - Provider for omnibox query tile suggestions.
+
+
+## Test and debug
+
+### Feature flags
+In chrome://flags,
+
+* Disable `Start surface`
+
+* Enable `Query tiles`
+
+* Enable `Query tiles in omnibox`
+
+* Set `Country code for getting tiles` to `IN` or `US`
+
+* If you’d like to see the UI immediately, enable `Query tile instant fetch`,
+restart Chrome twice and wait for 10 seconds.
+
+### WebUI
+Use `chrome://internals/query-tiles` to manually tune the flow(start/reset) and
+show the internal status and data.