Rename payments browser test target.

Having a target named "browsertests" means that trying to compile
browsertests from the command line, i.e.

  ninja -C out/Release browsertests

will work, when the user probably meant to type

  ninja -C out/Release browser_tests

So the name of the payments target is changed to browser_tests,
which is one of two conventions throughout the rest of Chrome.
(The other being myfeature_browsertests, which also avoids the
afore-mentioned issue.) Now if the user tries to compile
`browsertests`, they will see

  ninja: error: unknown target 'browsertests'

Bug: none
Change-Id: Ia6b679847744d7edfbfae3b0e20e395e9a4e226b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2574751
Auto-Submit: Evan Stade <estade@chromium.org>
Reviewed-by: Rouslan Solomakhin <rouslan@chromium.org>
Commit-Queue: Rouslan Solomakhin <rouslan@chromium.org>
Commit-Queue: Evan Stade <estade@chromium.org>
Cr-Commit-Position: refs/heads/master@{#834345}

chrome/browser/payments/BUILD.gn

@@ -2,7 +2,7 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-source_set("browsertests") {
+source_set("browser_tests") {
   testonly = true
 
   sources = [

chrome/test/BUILD.gn

@@ -540,7 +540,7 @@ if (is_android) {
       "//chrome:chrome_android_core",
       "//chrome/android:app_hooks_java",
       "//chrome/browser/metrics:test_support",
-      "//chrome/browser/payments:browsertests",
+      "//chrome/browser/payments:browser_tests",
       "//chrome/browser/privacy_budget:browser_tests",
       "//chrome/browser/profiling_host:profiling_browsertests",
       "//components/browser_ui/widget/android:java",
@@ -779,7 +779,7 @@ if (!is_android) {
       "//chrome/browser/image_decoder:browser_tests",
       "//chrome/browser/metrics:test_support",
       "//chrome/browser/notifications/scheduler/test:test_support",
-      "//chrome/browser/payments:browsertests",
+      "//chrome/browser/payments:browser_tests",
       "//chrome/browser/privacy_budget:browser_tests",
       "//chrome/browser/profiling_host:profiling_browsertests",
       "//chrome/browser/web_applications:browser_tests",