Improve ThemeService unit test robustness, and clean up.

* Fixes some (but not all) "Could not delete temp dir" warnings by adding a new
  ThemeScoper object.  This is the bulk of this change.
* Fixes some tests that failed on sytems with dark mode on by default.
* Cleans up some tests by removing unnecessary bits (e.g.
  UseDefaultTheme()/RunUntilIdle() calls on test start) and refactoring (e.g.
  adding a |theme_service_| convenience member alongside the existing
  |registry_|).

Bug: none
Change-Id: Ie5c3fcccda294a863c6a598a0513f076788b314d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1986284
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Auto-Submit: Peter Kasting <pkasting@chromium.org>
Reviewed-by: kylechar <kylechar@chromium.org>
Reviewed-by: Evan Stade <estade@chromium.org>
Cr-Commit-Position: refs/heads/master@{#728675}

base/files/scoped_temp_dir.cc

@@ -6,6 +6,7 @@
 
 #include "base/files/file_util.h"
 #include "base/logging.h"
+#include "base/macros.h"
 
 namespace base {
 
@@ -18,6 +19,16 @@ constexpr FilePath::CharType kScopedDirPrefix[] =
 
 ScopedTempDir::ScopedTempDir() = default;
 
+ScopedTempDir::ScopedTempDir(ScopedTempDir&& other) noexcept
+    : path_(other.Take()) {}
+
+ScopedTempDir& ScopedTempDir::operator=(ScopedTempDir&& other) {
+  if (!path_.empty() && !Delete())
+    DLOG(WARNING) << "Could not delete temp dir in operator=().";
+  path_ = other.Take();
+  return *this;
+}
+
 ScopedTempDir::~ScopedTempDir() {
   if (!path_.empty() && !Delete())
     DLOG(WARNING) << "Could not delete temp dir in dtor.";
@@ -75,9 +86,7 @@ bool ScopedTempDir::Delete() {
 }
 
 FilePath ScopedTempDir::Take() {
-  FilePath ret = path_;
-  path_ = FilePath();
-  return ret;
+  return std::exchange(path_, FilePath());
 }
 
 const FilePath& ScopedTempDir::GetPath() const {

base/files/scoped_temp_dir.h

@@ -18,8 +18,8 @@
 // intervening calls to Delete or Take, or the calls will fail.
 
 #include "base/base_export.h"
+#include "base/compiler_specific.h"
 #include "base/files/file_path.h"
-#include "base/macros.h"
 
 namespace base {
 
@@ -28,6 +28,9 @@ class BASE_EXPORT ScopedTempDir {
   // No directory is owned/created initially.
   ScopedTempDir();
 
+  ScopedTempDir(ScopedTempDir&&) noexcept;
+  ScopedTempDir& operator=(ScopedTempDir&&);
+
   // Recursively delete path.
   ~ScopedTempDir();
 
@@ -62,8 +65,6 @@ class BASE_EXPORT ScopedTempDir {
 
  private:
   FilePath path_;
-
-  DISALLOW_COPY_AND_ASSIGN(ScopedTempDir);
 };
 
 }  // namespace base

base/files/scoped_temp_dir_unittest.cc

@@ -94,6 +94,20 @@ TEST(ScopedTempDir, MultipleInvocations) {
   EXPECT_FALSE(other_dir.CreateUniqueTempDir());
 }
 
+TEST(ScopedTempDir, Move) {
+  ScopedTempDir dir;
+  EXPECT_TRUE(dir.CreateUniqueTempDir());
+  FilePath dir_path = dir.GetPath();
+  EXPECT_TRUE(DirectoryExists(dir_path));
+  {
+    ScopedTempDir other_dir(std::move(dir));
+    EXPECT_EQ(dir_path, other_dir.GetPath());
+    EXPECT_TRUE(DirectoryExists(dir_path));
+    EXPECT_FALSE(dir.IsValid());
+  }
+  EXPECT_FALSE(DirectoryExists(dir_path));
+}
+
 #if defined(OS_WIN)
 TEST(ScopedTempDir, LockedTempDir) {
   ScopedTempDir dir;