https://bugs.webkit.org/show_bug.cgi?id=117522

Reviewed by Darin Adler.

Add a new ActivityAssertion RAII class to handle allowing/disallowing
timer throttling.  Then make use of it during plugin initialisation
and destruction, as well as any synchronous messages (on the basis
that if another process is waiting for the plugin we shouldn't be
throttling timers).

* CMakeLists.txt:
* GNUmakefile.list.am:
* PluginProcess/WebProcessConnection.cpp:
(WebKit::WebProcessConnection::didReceiveSyncMessage):
(WebKit::WebProcessConnection::destroyPlugin):
(WebKit::WebProcessConnection::createPlugin):
* Shared/ActivityAssertion.cpp: Added.
(WebKit::ActivityAssertion::ActivityAssertion):
(WebKit::ActivityAssertion::~ActivityAssertion):
* Shared/ActivityAssertion.h: Added.
* Target.pri:
* WebKit2.xcodeproj/project.pbxproj:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@151480 268f45cc-cd09-0410-ab3c-d52691b4dbfc