cbui: don't check for overscroll in mac PWAs

The specific notion of overscroll this test is checking for is only
implemented on Aura platforms.

Bug: 1028239
Change-Id: Ic40d5d504e463517cd28fc28b3a6d36a7e5fb8a5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1946683Reviewed-by: Leonard Grey <lgrey@chromium.org>
Commit-Queue: Elly Fong-Jones <ellyjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#720549}

chrome/browser/ui/extensions/hosted_app_browsertest.cc

@@ -1389,7 +1389,13 @@ IN_PROC_BROWSER_TEST_P(SharedPWATest, InstallToShelfContainsAppName) {
 IN_PROC_BROWSER_TEST_P(HostedAppPWAOnlyTest, OverscrollEnabled) {
   ASSERT_TRUE(https_server()->Start());
   InstallSecurePWA();
+
+  // Overscroll is only enabled on Aura platforms currently.
+#if defined(USE_AURA)
   EXPECT_TRUE(app_browser_->CanOverscrollContent());
+#else
+  EXPECT_FALSE(app_browser_->CanOverscrollContent());
+#endif
 }
 
 // Tests that mixed content is not loaded inside PWA windows.