[WIP] Attempt to move everything cssom into a cssom namespace

third_party/WebKit/Source/core/css/cssom/MutableStylePropertyMap.h

Index: third_party/WebKit/Source/core/css/cssom/MutableStylePropertyMap.h
diff --git a/third_party/WebKit/Source/core/css/cssom/MutableStylePropertyMap.h b/third_party/WebKit/Source/core/css/cssom/MutableStylePropertyMap.h
index f7dd1b0f24aa7f82ed08e45e7767b51e5d5ccb91..340c5bd36e8dcea9604678da151b15f2de531f67 100644
--- a/third_party/WebKit/Source/core/css/cssom/MutableStylePropertyMap.h
+++ b/third_party/WebKit/Source/core/css/cssom/MutableStylePropertyMap.h
@@ -8,6 +8,7 @@
 #include "core/css/cssom/StylePropertyMap.h"
 
 namespace blink {
+namespace cssom {
 
 class CORE_EXPORT MutableStylePropertyMap : public StylePropertyMap {
     WTF_MAKE_NONCOPYABLE(MutableStylePropertyMap);
@@ -15,6 +16,8 @@ protected:
     MutableStylePropertyMap() = default;
 };
 
+} // namespace cssom
 } // namespace blink
 
+
 #endif