Rewrite blink_gc_plugin test script in Python.

tools/clang/blink_gc_plugin/CMakeLists.txt

 set(LIBRARYNAME BlinkGCPlugin)
 
 set(plugin_sources
   BlinkGCPlugin.cpp
   Edge.cpp
   RecordInfo.cpp)
 
 if(WIN32)
   # Clang doesn't support loadable modules on Windows. Unfortunately, building
   # the plugin as a static library and linking clang against it doesn't work.
   # Since clang doesn't reference any symbols in our static library, the linker
   # strips it out completely.
   # Instead, we rely on the fact that the SOURCES property of a target is no
   # read-only after CMake 3.1 and use it to compile the plugin directly into
   # clang...
   cmake_minimum_required(VERSION 3.1)
   # Paths must be absolute, since we're modifying a target in another directory.
   set(absolute_sources "")
   foreach(source ${plugin_sources})
     list(APPEND absolute_sources ${CMAKE_CURRENT_SOURCE_DIR}/${source})
   endforeach()
   set_property(TARGET clang APPEND PROPERTY SOURCES ${absolute_sources})
 else()
   add_llvm_loadable_module("lib${LIBRARYNAME}" ${plugin_sources})
   add_dependencies("lib${LIBRARYNAME}" clang)
 
   cr_install(TARGETS "lib${LIBRARYNAME}" LIBRARY DESTINATION lib)
 
   cr_add_test(blink_gc_plugin_test
-    ${CMAKE_CURRENT_SOURCE_DIR}/tests/test.sh
+    python
+    ${CMAKE_CURRENT_SOURCE_DIR}/tests/test.py
     ${CMAKE_BINARY_DIR}/bin/clang
     $<TARGET_FILE:lib${LIBRARYNAME}>
     )
 endif()