HID: Support top-level collection usages in device info.

device/hid/hid_report_descriptor.cc

Index: device/hid/hid_report_descriptor.cc
diff --git a/device/hid/hid_report_descriptor.cc b/device/hid/hid_report_descriptor.cc
new file mode 100644
index 0000000000000000000000000000000000000000..f2cb0f4901f10419b16079c372e2391d7d4bd40b
--- /dev/null
+++ b/device/hid/hid_report_descriptor.cc
@@ -0,0 +1,61 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "device/hid/hid_report_descriptor.h"
+
+#include "base/stl_util.h"
+
+namespace device {
+
+HidReportDescriptor::HidReportDescriptor(const uint8_t* bytes, size_t size) {
+  size_t header_index = 0;
+  HidReportDescriptorItem* item = NULL;
+  while (header_index < size) {
+    item = new HidReportDescriptorItem(&bytes[header_index], item);
+    items_.push_back(linked_ptr<HidReportDescriptorItem>(item));
+    header_index += item->GetSize();
+  }
+}
+
+HidReportDescriptor::~HidReportDescriptor() {}
+
+void HidReportDescriptor::GetTopLevelCollections(
+    std::vector<HidUsageAndPage>* topLevelCollections) {
+  DCHECK(topLevelCollections);
+  STLClearObject(topLevelCollections);
+
+  for (std::vector<linked_ptr<HidReportDescriptorItem> >::const_iterator
+           items_iter = items().begin();
+       items_iter != items().end();
+       ++items_iter) {
+    linked_ptr<HidReportDescriptorItem> item = *items_iter;
+
+    bool isTopLevelCollection =
+        item->tag() == HidReportDescriptorItem::kTagCollection &&
+        item->parent() == NULL;
+
+    if (isTopLevelCollection) {
+      uint16_t collection_usage = 0;
+      HidUsageAndPage::Page collection_usage_page =
+          HidUsageAndPage::kPageUndefined;
+
+      HidReportDescriptorItem* usage = item->previous();
+      if (usage && usage->tag() == HidReportDescriptorItem::kTagUsage) {
+        collection_usage = usage->GetShortData();
+      }
+
+      HidReportDescriptorItem* usage_page = usage->previous();
+      if (usage_page &&
+          usage_page->tag() == HidReportDescriptorItem::kTagUsagePage) {
+        collection_usage_page =
+            (HidUsageAndPage::Page)usage_page->GetShortData();
+      }
+
+      topLevelCollections->push_back(
+          HidUsageAndPage(collection_usage, collection_usage_page));
+    }
+  }
+}
+
+}  // namespace device