Rename StyleSheetCollections to StyleEngine.

Source/core/core.gypi

 {
     'variables': {
         'deprecated_perl_core_idl_files': [
             'css/CSS.idl',
             'css/CSSCharsetRule.idl',
             'css/CSSFontFaceLoadEvent.idl',
             'css/CSSFontFaceRule.idl',
             'css/CSSHostRule.idl',
             'css/CSSImportRule.idl',
             'css/CSSKeyframeRule.idl',
@@ skipping 1981 matching lines @@
             'dom/ShadowTreeStyleSheetCollection.cpp',
             'dom/ShadowTreeStyleSheetCollection.h',
             'dom/SimulatedClickOptions.h',
             'dom/SpaceSplitString.cpp',
             'dom/StaticNodeList.cpp',
             'dom/StaticNodeList.h',
             'dom/StringCallback.cpp',
             'dom/StringCallback.h',
             'dom/StyleElement.cpp',
             'dom/StyleElement.h',
+            'dom/StyleEngine.cpp',
+            'dom/StyleEngine.h',
             'dom/StyleSheetCollection.cpp',
             'dom/StyleSheetCollection.h',
-            'dom/StyleSheetCollections.cpp',
-            'dom/StyleSheetCollections.h',
             'dom/StyleSheetScopingNodeList.cpp',
             'dom/StyleSheetScopingNodeList.h',
             'dom/TagNodeList.cpp',
             'dom/TagNodeList.h',
             'dom/Text.cpp',
             'dom/TextEvent.cpp',
             'dom/TextEvent.h',
             'dom/TextLinkColors.cpp',
             'dom/TextLinkColors.h',
             'dom/Touch.cpp',
@@ skipping 1871 matching lines @@
                 'bison_exe': 'bison',
                 # We specify a preprocess so it happens locally and won't get
                 # distributed to goma.
                 # FIXME: /usr/bin/gcc won't exist on OSX forever. We want to
                 # use /usr/bin/clang once we require Xcode 4.x.
                 'preprocessor': '--preprocessor "/usr/bin/gcc -E -P -x c++"'
               }],
          ],
     }
 }