Add MemoryPurgeController

Source/platform/blink_platform.gypi

 {
   'includes': [
     'platform_generated.gypi',
   ],
   'variables': {
     'platform_files': [
       'AsyncFileSystemCallbacks.h',
       'CalculationValue.h',
       'CheckedInt.h',
       'Clock.cpp',
@@ skipping 52 matching lines @@
       'LifecycleNotifier.h',
       'LifecycleObserver.h',
       'LinkHash.cpp',
       'LinkHash.h',
       'Logging.cpp',
       'Logging.h',
       'MIMETypeFromURL.cpp',
       'MIMETypeFromURL.h',
       'MIMETypeRegistry.cpp',
       'MIMETypeRegistry.h',
+      'MemoryPurgeController.cpp',
+      'MemoryPurgeController.h',
       'NotImplemented.cpp',
       'NotImplemented.h',
       'PartitionAllocMemoryDumpProvider.cpp',
       'PartitionAllocMemoryDumpProvider.h',
       'PODArena.h',
       'PODFreeListArena.h',
       'PODInterval.h',
       'PODIntervalTree.h',
       'PODRedBlackTree.h',
       'ParsingUtilities.h',
@@ skipping 971 matching lines @@
       ['os_posix==1 and OS!="mac"',
         {
           'platform_test_files': [
             'text/LocaleICUTest.cpp',
           ],
         }
       ],
     ],
   },
 }