Add initial support for API versioning (see #3836)

- Generated files are now created when running cef_create_projects or
  the new version_manager.py tool. These files are still created in the
  cef/ source tree (same location as before) but Git ignores them due to
  the generated .gitignore file.
- API hashes are committed to Git as a new cef_api_versions.json file.
  This file is used for both code generation and CEF version calculation
  (replacing the previous usage of cef_api_hash.h for this purpose).
  It will be updated by the CEF admin before merging breaking API
  changes upstream.
- As an added benefit to the above, contributor PRs will no longer
  contain generated code that is susceptible to frequent merge conflicts.
- From a code generation perspective, the main difference is that we now
  use versioned structs (e.g. cef_browser_0_t instead of cef_browser_t)
  on the libcef (dll/framework) side. Most of the make_*.py tool changes
  are related to supporting this.
- From the client perspective, you can now define CEF_API_VERSION in the
  project configuration (or get CEF_EXPERIMENTAL by default). This
  define will change the API exposed in CEF’s include/ and include/capi
  header files. All client-side targets including libcef_dll_wrapper
  will need be recompiled when changing this define.
- Examples of the new API-related define usage are provided in
  cef_api_version_test.h, api_version_test_impl.cc and
  api_version_unittest.cc.

To test:
- Run `ceftests --gtest_filter=ApiVersionTest.*`
- Add `cef_api_version=13300` to GN_DEFINES. Re-run configure, build and
  ceftests steps.
- Repeat with 13301, 13302, 13303 (all supported test versions).

libcef/common/test/translator_test_impl.cc

@@ -4,6 +4,8 @@
 
 #include "cef/include/test/cef_translator_test.h"
 
+namespace {
+
 class CefTranslatorTestRefPtrLibraryImpl
     : public CefTranslatorTestRefPtrLibrary {
  public:
@@ -18,19 +20,22 @@ class CefTranslatorTestRefPtrLibraryImpl
 
   void SetValue(int value) override { value_ = value; }
 
- protected:
+ private:
   int value_;
 
- private:
   IMPLEMENT_REFCOUNTING(CefTranslatorTestRefPtrLibraryImpl);
 };
 
+}  // namespace
+
 // static
 CefRefPtr<CefTranslatorTestRefPtrLibrary>
 CefTranslatorTestRefPtrLibrary::Create(int value) {
   return new CefTranslatorTestRefPtrLibraryImpl(value);
 }
 
+namespace {
+
 class CefTranslatorTestRefPtrLibraryChildImpl
     : public CefTranslatorTestRefPtrLibraryChild {
  public:
@@ -50,20 +55,23 @@ class CefTranslatorTestRefPtrLibraryChildImpl
 
   void SetOtherValue(int value) override { other_value_ = value; }
 
- protected:
+ private:
   int value_;
   int other_value_;
 
- private:
   IMPLEMENT_REFCOUNTING(CefTranslatorTestRefPtrLibraryChildImpl);
 };
 
+}  // namespace
+
 // static
 CefRefPtr<CefTranslatorTestRefPtrLibraryChild>
 CefTranslatorTestRefPtrLibraryChild::Create(int value, int other_value) {
   return new CefTranslatorTestRefPtrLibraryChildImpl(value, other_value);
 }
 
+namespace {
+
 class CefTranslatorTestRefPtrLibraryChildChildImpl
     : public CefTranslatorTestRefPtrLibraryChildChild {
  public:
@@ -91,15 +99,16 @@ class CefTranslatorTestRefPtrLibraryChildChildImpl
 
   void SetOtherOtherValue(int value) override { other_other_value_ = value; }
 
- protected:
+ private:
   int value_;
   int other_value_;
   int other_other_value_;
 
- private:
   IMPLEMENT_REFCOUNTING(CefTranslatorTestRefPtrLibraryChildChildImpl);
 };
 
+}  // namespace
+
 // static
 CefRefPtr<CefTranslatorTestRefPtrLibraryChildChild>
 CefTranslatorTestRefPtrLibraryChildChild::Create(int value,
@@ -109,6 +118,8 @@ CefTranslatorTestRefPtrLibraryChildChild::Create(int value,
                                                           other_other_value);
 }
 
+namespace {
+
 class CefTranslatorTestScopedLibraryImpl
     : public CefTranslatorTestScopedLibrary {
  public:
@@ -123,10 +134,12 @@ class CefTranslatorTestScopedLibraryImpl
 
   void SetValue(int value) override { value_ = value; }
 
- protected:
+ private:
   int value_;
 };
 
+}  // namespace
+
 // static
 CefOwnPtr<CefTranslatorTestScopedLibrary>
 CefTranslatorTestScopedLibrary::Create(int value) {
@@ -134,6 +147,8 @@ CefTranslatorTestScopedLibrary::Create(int value) {
       new CefTranslatorTestScopedLibraryImpl(value));
 }
 
+namespace {
+
 class CefTranslatorTestScopedLibraryChildImpl
     : public CefTranslatorTestScopedLibraryChild {
  public:
@@ -153,11 +168,13 @@ class CefTranslatorTestScopedLibraryChildImpl
 
   void SetOtherValue(int value) override { other_value_ = value; }
 
- protected:
+ private:
   int value_;
   int other_value_;
 };
 
+}  // namespace
+
 // static
 CefOwnPtr<CefTranslatorTestScopedLibraryChild>
 CefTranslatorTestScopedLibraryChild::Create(int value, int other_value) {
@@ -165,6 +182,8 @@ CefTranslatorTestScopedLibraryChild::Create(int value, int other_value) {
       new CefTranslatorTestScopedLibraryChildImpl(value, other_value));
 }
 
+namespace {
+
 class CefTranslatorTestScopedLibraryChildChildImpl
     : public CefTranslatorTestScopedLibraryChildChild {
  public:
@@ -192,12 +211,14 @@ class CefTranslatorTestScopedLibraryChildChildImpl
 
   void SetOtherOtherValue(int value) override { other_other_value_ = value; }
 
- protected:
+ private:
   int value_;
   int other_value_;
   int other_other_value_;
 };
 
+}  // namespace
+
 // static
 CefOwnPtr<CefTranslatorTestScopedLibraryChildChild>
 CefTranslatorTestScopedLibraryChildChild::Create(int value,
@@ -208,6 +229,8 @@ CefTranslatorTestScopedLibraryChildChild::Create(int value,
                                                        other_other_value));
 }
 
+namespace {
+
 class CefTranslatorTestImpl : public CefTranslatorTest {
  public:
   CefTranslatorTestImpl() = default;
@@ -595,6 +618,8 @@ class CefTranslatorTestImpl : public CefTranslatorTest {
   IMPLEMENT_REFCOUNTING(CefTranslatorTestImpl);
 };
 
+}  // namespace
+
 // static
 CefRefPtr<CefTranslatorTest> CefTranslatorTest::Create() {
   return new CefTranslatorTestImpl();