Use LocalStyleChange for content:attr() changes.

LocalStyleChange should be sufficient for updating pseudo elements when
attributes affecting the content property changes.

Review URL: https://codereview.chromium.org/609813002

git-svn-id: svn://svn.chromium.org/blink/trunk@182830 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Refactor interface.cpp and interface_base.cpp for partial interface modularization.

Design Doc (partial interface modularization):
https://docs.google.com/a/chromium.org/document/d/1TpqG_bWJfHFo6swv5zbqfjxHl_K31C307NvdyF1NAcU/edit?usp=sharing

partial_interface.cpp will be added for partial interfaces defined in component: modules.

interface_base.cpp is the base template of interface.cpp and partial_interface.cpp.
So, code shared by interface.cpp and partial_interface.cpp should be moved to interface_base.cpp.

BUG=358074

Review URL: https://codereview.chromium.org/612563003

git-svn-id: svn://svn.chromium.org/blink/trunk@182831 bbb929c8-8fbe-4397-9dbb-9b2b20218538