Add API tests for the chrome.hid API.

These test validate that the implementation of the chrome.hid API is using
the API provided by //device/hid correctly. It does not talk to real devices
or validate platform-specific functionality.

BUG=

Review URL: https://codereview.chromium.org/690473002

Cr-Commit-Position: refs/heads/master@{#302117}

1 files changed, 8 insertions, 1 deletions

diff --git a/device/hid/hid_service.cc b/device/hid/hid_service.cc
index d2ccaa3..071b396 100644
--- a/device/hid/hid_service.cc
+++ b/device/hid/hid_service.cc
@@ -55,7 +55,7 @@ HidService* HidService::GetInstance(
 #elif defined(OS_WIN)
     g_service = new HidServiceWin();
 #endif
-    if (g_service != NULL) {
+    if (g_service != nullptr) {
       Destroyer* destroyer = new Destroyer(g_service);
       base::MessageLoop::current()->AddDestructionObserver(destroyer);
     }
@@ -63,6 +63,13 @@ HidService* HidService::GetInstance(
   return g_service;
 }
 
+void HidService::SetInstanceForTest(HidService* instance) {
+  DCHECK(!g_service);
+  g_service = instance;
+  Destroyer* destroyer = new Destroyer(g_service);
+  base::MessageLoop::current()->AddDestructionObserver(destroyer);
+}
+
 HidService::~HidService() {
   DCHECK(thread_checker_.CalledOnValidThread());
 }