HTMLScriptElement::setText should use AttachLazily

In addition to switching setText to use AttachLazily I factored out the
checks for a single text node child used here and inside markup.cpp to
be shared.

Review URL: https://chromiumcodereview.appspot.com/22966008

git-svn-id: svn://svn.chromium.org/blink/trunk@156382 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Add tests to validate background bending with the following properties:
1. Blend a background image and a background color specifying background-position in percentage, such as 50% 50% 
2. Blend a background image and a background color specifying background-size in pixels 
3. Blend a background image and a background color specifying background-size in percentage 
4. Blend a background image and a background color specifying background-size: cover 
5. Blend a background image and a background color specifying background-size: contain 
6. Blend a background image and a background color specifying background-repeat: no-repeat 
7. Blend a background image and a background color specifying background-clip: padding-box 
8. Blend a background image and a background color specifying background-clip: content-box 
9. Blend a background image and a background color specifying background-origin: border-box 
10. Blend a background image and a background color specifying background-origin: content-box 
11. Blend a background image and a background color specifying background-attachment: fixed

BUG=256613

Review URL: https://chromiumcodereview.appspot.com/23154003

git-svn-id: svn://svn.chromium.org/blink/trunk@156383 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Convert 'FileError::throwDOMException' to use 'ExceptionState::throwSecurityError'

The message is still uninteresting, but the sooner we get all
SecurityError callsites migrated to the new API, the sooner we can start
ASSERTing that it's the only way to throw SecurityError.

BUG=275282
R=kinuko@chromium.org

Review URL: https://codereview.chromium.org/22813004

git-svn-id: svn://svn.chromium.org/blink/trunk@156384 bbb929c8-8fbe-4397-9dbb-9b2b20218538