Introduce TextFinder class for decoupling WebFrameImpl and text finder.

Source/web/web.gypi

 {
   'variables': {
     'web_files': [
       'AssertMatchingEnums.cpp',
       'AssociatedURLLoader.cpp',
       'AssociatedURLLoader.h',
       'BackForwardClientImpl.cpp',
       'BackForwardClientImpl.h',
       'ChromeClientImpl.cpp',
       'ChromeClientImpl.h',
@@ skipping 75 matching lines @@
       'SpeechInputClientImpl.cpp',
       'SpeechInputClientImpl.h',
       'SpeechRecognitionClientProxy.cpp',
       'SpeechRecognitionClientProxy.h',
       'SpellCheckerClientImpl.cpp',
       'SpellCheckerClientImpl.h',
       'StorageClientImpl.cpp',
       'StorageClientImpl.h',
       'StorageQuotaClientImpl.cpp',
       'StorageQuotaClientImpl.h',
+      'TextFinder.cpp',
+      'TextFinder.h',
       'UserMediaClientImpl.cpp',
       'UserMediaClientImpl.h',
       'ValidationMessageClientImpl.cpp',
       'ValidationMessageClientImpl.h',
       'ViewportAnchor.cpp',
       'ViewportAnchor.h',
       'WebAXObject.cpp',
       'WebArrayBufferConverter.cpp',
       'WebArrayBufferView.cpp',
       'WebBindings.cpp',
@@ skipping 244 matching lines @@
         {
           'web_unittest_files': [
             'tests/KeyCodeConversionTestGtk.cpp',
             'tests/WebInputEventFactoryTestGtk.cpp',
           ],
         }
       ],
     ],
   },
 }