Create fewer tiles when page is loading
https://bugs.webkit.org/show_bug.cgi?id=114294

Source/WebCore:

Reviewed by Anders Carlsson.

We currently create speculative tiles immediately. Page is often changing rapidly during loading and
keeping the speculative tiles up to date creates extra work.

Tests: platform/mac-wk2/tiled-drawing/tile-coverage-after-scroll-speculative.html
       platform/mac-wk2/tiled-drawing/tile-coverage-speculative.html

       * loader/FrameLoader.cpp:
(WebCore::FrameLoader::loadProgressingStatusChanged):
* page/FrameView.cpp:
(WebCore::FrameView::adjustTiledBackingCoverage):
(WebCore::FrameView::setWasScrolledByUser):

    User scrolling enables speculative tiling no matter what the load status.

* page/FrameView.h:
* rendering/RenderLayerBacking.cpp:
(WebCore::computeTileCoverage):
(WebCore::RenderLayerBacking::adjustTiledBackingCoverage):

    Cover only the viewport during loading.

LayoutTests:

Reviewed by Anders Carlsson.

Reduced initial tile counts and new tests for speculative tiles.

* platform/mac-wk2/tiled-drawing/fixed-background/fixed-background-no-image-expected.txt:
* platform/mac-wk2/tiled-drawing/tile-coverage-after-scroll-expected.txt:
* platform/mac-wk2/tiled-drawing/tile-coverage-after-scroll-speculative-expected.txt: Added.
* platform/mac-wk2/tiled-drawing/tile-coverage-after-scroll-speculative.html: Added.
* platform/mac-wk2/tiled-drawing/tile-coverage-scroll-to-bottom-expected.txt:
* platform/mac-wk2/tiled-drawing/tile-coverage-speculative-expected.txt: Added.
* platform/mac-wk2/tiled-drawing/tile-coverage-speculative.html: Added.
* platform/mac-wk2/tiled-drawing/tiled-drawing-zoom-expected.txt:
* platform/mac-wk2/tiled-drawing/tiled-drawing-zoom-scrolled-expected.txt:
* platform/mac-wk2/tiled-drawing/use-tiled-drawing-expected.txt:
* platform/mac/platform/mac-wk2/tiled-drawing/fixed-background/fixed-body-background-body-layer-expected.txt:
* platform/mac/platform/mac-wk2/tiled-drawing/fixed-background/fixed-body-background-expected.txt:
* platform/mac/platform/mac-wk2/tiled-drawing/fixed-background/fixed-body-background-opacity-html-expected.txt:
* platform/mac/platform/mac-wk2/tiled-drawing/fixed-background/fixed-body-background-positioned-expected.txt:
* platform/mac/platform/mac-wk2/tiled-drawing/fixed-background/fixed-body-background-transformed-html-expected.txt:
* platform/mac/platform/mac-wk2/tiled-drawing/fixed-background/fixed-body-background-zoomed-expected.txt:
* platform/mac/platform/mac-wk2/tiled-drawing/fixed-background/fixed-html-background-expected.txt:


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@148089 268f45cc-cd09-0410-ab3c-d52691b4dbfc