Add unit tests for TabGridItemTouchHelperCallback

Bug: 978236
Change-Id: If2bd37ed4182597e7ee0175f367604b9ec2bca42
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1674669Reviewed-by: Wei-Yin Chen (陳威尹) <wychen@chromium.org>
Reviewed-by: Yusuf Ozuysal <yusufo@chromium.org>
Commit-Queue: Yue Zhang <yuezhanggg@google.com>
Cr-Commit-Position: refs/heads/master@{#672155}

chrome/android/features/tab_ui/tab_management_java_sources.gni

@@ -20,5 +20,6 @@ tab_management_test_java_sources = [
 
 tab_management_junit_java_sources = [
   "//chrome/android/features/tab_ui/junit/src/org/chromium/chrome/browser/tasks/tab_management/GridTabSwitcherMediatorUnitTest.java",
+  "//chrome/android/features/tab_ui/junit/src/org/chromium/chrome/browser/tasks/tab_management/TabGridItemTouchHelperCallbackUnitTest.java",
   "//chrome/android/features/tab_ui/junit/src/org/chromium/chrome/browser/tasks/tab_management/TabListMediatorUnitTest.java",
 ]