Get rid of RenderBox's overrideWidth/overrideHeight maps.

Instead of HashMaps, use RenderBoxRareData. That way, we just pay the malloc
cost the first time we use an override size instead of multiple hash
table operations per layout of each flex item.

Since we already were using a pointer for the rare m_inlineBoxWrapper,
adding the rare data pointer doesn't increase our memory use in the common case.

These were showing up as ~1-2% of the layout time in the 
infinite_scrolling benchmark in the key silk pageset.

Review URL: https://codereview.chromium.org/151953002

git-svn-id: svn://svn.chromium.org/blink/trunk@166737 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Move Clipboard-related code from core/dom to core/clipboard

A lot of this stuff landed in dom when it was ousted from core/platform; most of
these classes would be happier in blink_platform (save for Clipboard,
DataTransferItem, and DataTransferItemList, which all have associated IDL files),
but due to a few File dependencies it's not trivial to move there.

But since it doesn't belong in dom (they're not related to Document structure),
a new clipboard directory seems the best bet.

R=abarth@chromium.org

Review URL: https://codereview.chromium.org/153343003

git-svn-id: svn://svn.chromium.org/blink/trunk@166738 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Fix potential crash causes in ServiceWorker LayoutTests

1. Adds an empty serviceworker.js
Registering nonexistent worker script will start to return InstallError,
so create an empty serviceworker.js in the LayoutTests (we should also
add nonexistent worker case once the registration patch re-lands)

2. Handle all possible error cases in ServiceWorkerError.cpp
Getting an error other than DisabledError hits ASSERT in debug build, so
handle other error cases too.

BUG=285976
TEST=virtual/serviceworker/http/tests/serviceworker/registration.html

Review URL: https://codereview.chromium.org/157273005

git-svn-id: svn://svn.chromium.org/blink/trunk@166739 bbb929c8-8fbe-4397-9dbb-9b2b20218538