Add unittests target to the binary distribution (issue #1632)

- Move all tests from the top-level directory to tests/.
- Move files shared by cefclient and unittests to tests/shared/.
- Add a fused (single header/source file) version of gtest in
  tests/gtest/ with associated CMake configuration.
- Test-only headers are now exposed in include/test/. Unit test
  targets must define UNIT_TEST in order to access them.
- Replace usage of USING_CEF_SHARED with WRAPPING_CEF_SHARED for
  clarity (only the libcef_dll_wrapper target should define it).
- Remove the RENAME_DIRECTORY CMake macro which is no longer used.
- Remove C++11 usage from unittests sources for compatibility with
  the binary distribution configuration.
- Windows: Fix build errors due to chrome_elf.dll and imm32.lib
  missing from the CMake configuration.

tools/make_capi_header.py

@@ -87,6 +87,17 @@ def make_capi_header(header, filename):
 #pragma once
 
 """
+
+    # Protect against incorrect use of test headers.
+    if filename.startswith('test/'):
+      result += \
+"""#if !defined(BUILDING_CEF_SHARED) && !defined(WRAPPING_CEF_SHARED) && \\
+    !defined(UNIT_TEST)
+#error This file can be included for unit tests only
+#endif
+
+"""
+
     classes = header.get_classes(filename)
 
     # identify all includes and forward declarations