Web Inspector: show image decode performed off main thread on timeline
https://bugs.webkit.org/show_bug.cgi?id=111159

Reviewed by Pavel Feldman.

- add handling of Decode Image event to TimelineTraceEventProcessorr;
- only log platform events for the main thread;
- extract constants for trace events produced by platform instrumentation.

* inspector/InspectorTimelineAgent.cpp:
(TimelineRecordType):
* inspector/InspectorTimelineAgent.h:
(TimelineRecordType):
* inspector/TimelineTraceEventProcessor.cpp:
(WebCore::TimelineTraceEventProcessor::TimelineTraceEventProcessor):
(WebCore::TimelineTraceEventProcessor::onImageDecodeBegin):
(WebCore):
(WebCore::TimelineTraceEventProcessor::onImageDecodeEnd):
* inspector/TimelineTraceEventProcessor.h:
(TimelineTraceEventProcessor):
* platform/PlatformInstrumentation.cpp:
(WebCore):
* platform/PlatformInstrumentation.h:
(PlatformInstrumentation):
(WebCore):
(WebCore::PlatformInstrumentation::willDecodeImage):
(WebCore::PlatformInstrumentation::didDecodeImage):
(WebCore::PlatformInstrumentation::willResizeImage):
(WebCore::PlatformInstrumentation::didResizeImage):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@145889 268f45cc-cd09-0410-ab3c-d52691b4dbfc