Add base::Value::AsDictionaryValue().

This is an adaptor to allow a caller to use base::Value instead of
base::DictionaryValue to construct a dictionary value, and able to
easily pass the value to a function that still expects const
base::DictionaryValue&. This makes it easier to move away from
base::DictionaryValue in smaller increments. Use it in one place to
demonstrate it works.

Do the same for list values with base::Value::AsListValue().

Bug: 646113
Change-Id: I9116525ef5a5a80d3752cdca1960d21b2288ff42
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1838684Reviewed-by: Paul Jensen <pauljensen@chromium.org>
Reviewed-by: Jan Wilken Dörrie <jdoerrie@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#703845}

base/values.cc

@@ -147,6 +147,18 @@ std::unique_ptr<Value> Value::ToUniquePtrValue(Value val) {
   return std::make_unique<Value>(std::move(val));
 }
 
+// static
+const DictionaryValue& Value::AsDictionaryValue(const Value& val) {
+  CHECK(val.is_dict());
+  return static_cast<const DictionaryValue&>(val);
+}
+
+// static
+const ListValue& Value::AsListValue(const Value& val) {
+  CHECK(val.is_list());
+  return static_cast<const ListValue&>(val);
+}
+
 Value::Value(Value&& that) noexcept {
   InternalMoveConstructFrom(std::move(that));
 }

base/values.h

@@ -111,6 +111,8 @@ class BASE_EXPORT Value {
   // Adaptors for converting from the old way to the new way and vice versa.
   static Value FromUniquePtrValue(std::unique_ptr<Value> val);
   static std::unique_ptr<Value> ToUniquePtrValue(Value val);
+  static const DictionaryValue& AsDictionaryValue(const Value& val);
+  static const ListValue& AsListValue(const Value& val);
 
   Value(Value&& that) noexcept;
   Value() noexcept {}  // A null value

chrome/browser/ui/webui/print_preview/print_preview_handler_unittest.cc

@@ -701,7 +701,7 @@ TEST_F(PrintPreviewHandlerTest, SendPreviewUpdates) {
 
   // Simulate renderer responses: PageLayoutReady, PageCountReady,
   // PagePreviewReady, and OnPrintPreviewReady will be called in that order.
-  base::DictionaryValue layout;
+  base::Value layout(base::Value::Type::DICTIONARY);
   layout.SetDoubleKey(kSettingMarginTop, 34.0);
   layout.SetDoubleKey(kSettingMarginLeft, 34.0);
   layout.SetDoubleKey(kSettingMarginBottom, 34.0);
@@ -712,7 +712,8 @@ TEST_F(PrintPreviewHandlerTest, SendPreviewUpdates) {
   layout.SetIntKey(kSettingPrintableAreaY, 17);
   layout.SetIntKey(kSettingPrintableAreaWidth, 578);
   layout.SetIntKey(kSettingPrintableAreaHeight, 734);
-  handler()->SendPageLayoutReady(layout, /*has_custom_page_size_style,=*/false,
+  handler()->SendPageLayoutReady(base::Value::AsDictionaryValue(layout),
+                                 /*has_custom_page_size_style,=*/false,
                                  preview_request_id);
 
   // Verify that page-layout-ready webUI event was fired.

components/cronet/host_cache_persistence_manager_unittest.cc

@@ -45,14 +45,14 @@ class HostCachePersistenceManagerTest : public testing::Test {
   // not the full contents, since the tests in this file are only intended
   // to test that writes happen when they're supposed to, not serialization
   // correctness.
-  void CheckPref(size_t size) {
+  void CheckPref(size_t expected_size) {
     const base::Value* value = pref_service_->GetUserPref(kPrefName);
-    base::ListValue list;
+    base::Value list(base::Value::Type::LIST);
     if (value)
-      list = base::ListValue(value->GetList());
+      list = base::Value(value->GetList());
     net::HostCache temp_cache(10);
-    temp_cache.RestoreFromListValue(list);
-    ASSERT_EQ(size, temp_cache.size());
+    temp_cache.RestoreFromListValue(base::Value::AsListValue(list));
+    ASSERT_EQ(expected_size, temp_cache.size());
   }
 
   // Generates a temporary HostCache with a few entries and uses it to