arc: Fix ArcVmClientAdapterTest.ChromeOsChannel* unittests

This change fixes ArcVmClientAdapterTest.ChromeOsChannel{Stable,Unknown}
by adding a call to base::SysInfo::ResetChromeOSVersionInfoForTest().
This fixes a crash in base::SysInfo::SetChromeOSVersionInfoForTest that
happens when it is called twice without being reset.

BUG=b:174186047
TEST=ArcVmClientAdapterTest unittests

Change-Id: I5ba40f3efe5ddd44fbcf9ec7ec56711678c50248
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2559533
Auto-Submit: Willie Koomson <wvk@google.com>
Reviewed-by: Yusuke Sato <yusukes@chromium.org>
Commit-Queue: Yusuke Sato <yusukes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#831216}

components/arc/session/arc_vm_client_adapter_unittest.cc

@@ -1199,6 +1199,8 @@ TEST_F(ArcVmClientAdapterTest, ChromeOsChannelStable) {
   EXPECT_TRUE(
       base::Contains(GetTestConciergeClient()->start_arc_vm_request().params(),
                      "androidboot.chromeos_channel=stable"));
+
+  base::SysInfo::ResetChromeOSVersionInfoForTest();
 }
 
 TEST_F(ArcVmClientAdapterTest, ChromeOsChannelUnknown) {
@@ -1212,6 +1214,8 @@ TEST_F(ArcVmClientAdapterTest, ChromeOsChannelUnknown) {
   EXPECT_TRUE(
       base::Contains(GetTestConciergeClient()->start_arc_vm_request().params(),
                      "androidboot.chromeos_channel=unknown"));
+
+  base::SysInfo::ResetChromeOSVersionInfoForTest();
 }
 
 // Tests that the binary translation type is set to None when no library is