Revert "Disable SessionRestoreTest.MemoryPressureLoadsNotAllTabs on CrOS"

This reverts commit ced45ea8.

Reason for revert: Concurrently a suspicious CL has been reverted: 
https://chromium-review.googlesource.com/c/chromium/src/+/1125459


Original change's description:
> Disable SessionRestoreTest.MemoryPressureLoadsNotAllTabs on CrOS
> 
> TBR=sky@chromium.org
> NOTRY=true
> 
> Bug: 860111
> Change-Id: Ida98cb932b4caf9ffb60622a293dfd2da6b5c29d
> Reviewed-on: https://chromium-review.googlesource.com/1125540
> Reviewed-by: Makoto Shimazu <shimazu@chromium.org>
> Commit-Queue: Makoto Shimazu <shimazu@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#572451}

TBR=sky@chromium.org,shimazu@chromium.org

Change-Id: I3b5b6a885e76e6090c87873880836b7bb3c344f4
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 860111
Reviewed-on: https://chromium-review.googlesource.com/1125559Reviewed-by: Makoto Shimazu <shimazu@chromium.org>
Commit-Queue: Makoto Shimazu <shimazu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#572476}

chrome/browser/sessions/session_restore_browsertest.cc

@@ -939,15 +939,7 @@ IN_PROC_BROWSER_TEST_F(SessionRestoreTest, NoMemoryPressureLoadsAllTabs) {
       tab_strip_model->GetWebContentsAt(2)->GetRenderWidgetHostView());
 }
 
-// Disable on CrOS since it's flaky: crbug.com/860111.
-#if defined(OS_CHROMEOS)
-#define MAYBE_MemoryPressureLoadsNotAllTabs \
-  DISABLED_MemoryPressureLoadsNotAllTabs
-#else
-#define MAYBE_MemoryPressureLoadsNotAllTabs MemoryPressureLoadsNotAllTabs
-#endif
-IN_PROC_BROWSER_TEST_F(SessionRestoreTest,
-                       MAYBE_MemoryPressureLoadsNotAllTabs) {
+IN_PROC_BROWSER_TEST_F(SessionRestoreTest, MemoryPressureLoadsNotAllTabs) {
   // Add several tabs to the browser. Restart the browser and check that all
   // tabs got loaded properly.
   ui_test_utils::NavigateToURLWithDisposition(