Add a sanity DCHECK when constructing a UIResourceRequest.

Adds a DCHECK that we're actually deleting a resource when no bitmap
is specified in the constructor.

BUG=562353

CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_blink_rel

Review-Url: https://codereview.chromium.org/2154473004
Cr-Commit-Position: refs/heads/master@{#405906}

cc/resources/ui_resource_request.cc

@@ -10,7 +10,9 @@ namespace cc {
 
 UIResourceRequest::UIResourceRequest(UIResourceRequestType type,
                                      UIResourceId id)
-    : type_(type), id_(id) {}
+    : type_(type), id_(id) {
+  DCHECK(type == UI_RESOURCE_DELETE);
+}
 
 UIResourceRequest::UIResourceRequest(UIResourceRequestType type,
                                      UIResourceId id,