WTF: Make String's pretty-printing from gtest prettier.

This patch extends the content of WTFTestHelpers and updates String's
pretty-printing logic used by gtest so it would make more sense for
developers.

Most notably, the pretty printer now differentiates a null string from an empty
string, and also it is able to print control characters escaped.

Unit-test only patch; no behavior change expected.

BUG=none

Review URL: https://codereview.chromium.org/98153002

git-svn-id: svn://svn.chromium.org/blink/trunk@162953 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Move relayoutForPagination and addOverflowFromInlineChildren to RenderBlockFlow

Both functions are currently defined in RenderBlock, but only used by RenderBlockFlow
and its sub-classes (relayoutForPagination is used for multi-column blocks, and
only RenderBlockFlow deals with inline children).

BUG=302024

Review URL: https://codereview.chromium.org/98043002

git-svn-id: svn://svn.chromium.org/blink/trunk@162954 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Web Animations CSS: Fix crash when animating viewport units

This patch makes viewport units default to snapping behaviour when
mismatched instead of animating them smoothly, this matches legacy
animation behaviour.

BUG=322675

Review URL: https://codereview.chromium.org/90113003

git-svn-id: svn://svn.chromium.org/blink/trunk@162956 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Revert 162740 "Optimization in handleStyleSpans() for restrictin..."

I'm not sure why r162740 causes heap-use-after-free. The patch changes
to end of loop node before loop rather than every iteration. I would
like to see reverting r162740 fixes heap-use-after-free.

> Optimization in handleStyleSpans() for restricting the for loop to iterate only
> over the InsertedNodes (i.e. the inserted fragment).
> This is in line with other methods such as removeRedundantStylesAndKeepStyleSpanInline()
> and makeInsertedContentRoundTrippableWithHTMLTreeBuilder() that iterate over
> the InsertedNodes.
> 
> No existing test should fail with this patch.
> 
> Review URL: https://codereview.chromium.org/72743002

TBR=a.bah@samsung.com
BUG=324324

Review URL: https://codereview.chromium.org/98063003

git-svn-id: svn://svn.chromium.org/blink/trunk@162957 bbb929c8-8fbe-4397-9dbb-9b2b20218538