Check null position start of paragraph to move parameter in CompositeEditCommand::moveParagraph

This patch changes CompositeEditCommand::moveParagraph to check whether
|startOfParagraphToMove| is null position or not. If |startOfParagraphToMove|
is null position, |moveParagraph| does nothing as |startOfParagraphToMove|
equals to |destination|.

BUG=377709
TEST=LayoutTests/editing/execCommand/unlistify-body-crash.html

Review URL: https://codereview.chromium.org/303743003

git-svn-id: svn://svn.chromium.org/blink/trunk@175046 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Avoid to insert TAB before HTML element

This patch changes InsertTextCommand::insertTab before HTML element because
we can't set Text node as document element.

BUG=348209
TEST=LayoutTests/editing/execCommand/insert-tab-to-html-element-crash.html

Review URL: https://codereview.chromium.org/306583005

git-svn-id: svn://svn.chromium.org/blink/trunk@175047 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Fix toV8 with empty context in InspectorOverlay::overlayPage()

BUG=369451

Review URL: https://codereview.chromium.org/301663002

git-svn-id: svn://svn.chromium.org/blink/trunk@175048 bbb929c8-8fbe-4397-9dbb-9b2b20218538