Make DummyPageHolder to have all empty clients

This patch changes DummyPageHolder to use fillWithEmptyClients() instead of making specific empty clients for writing tests depending on client objects not created in current DumpPageHolder class, e.g. spell checker client for editing test.
 
BUG=n/a
TEST=n/a

Review URL: https://codereview.chromium.org/311263007

git-svn-id: svn://svn.chromium.org/blink/trunk@175563 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Skip traversing wholeSubtree subtrees with clean invalidation bits.

During style invalidation we need to continue to traverse a subtree that is
marked with SubtreeStyleChange to clear any remaining invalidation bits.
But, when the childNeedsInvalidation bit is not set, there should be no
bits left to clear in the subtree. Hence, we can skip traversing that
subtree.

R=esprehn@chromium.org,chrishtr@chromium.org
BUG=381062

Review URL: https://codereview.chromium.org/317133002

git-svn-id: svn://svn.chromium.org/blink/trunk@175564 bbb929c8-8fbe-4397-9dbb-9b2b20218538