WebIDL constants should be non configurable

Currently we make constants configurable. This change makes us
consistent with the WebIDL spec as well as with Firefox and IE.

BUG=300002

Review URL: https://chromiumcodereview.appspot.com/25109003

git-svn-id: svn://svn.chromium.org/blink/trunk@158475 bbb929c8-8fbe-4397-9dbb-9b2b20218538
[Android WebView] Fix bugs with initial-scale between 0 and 1

The fix in https://chromiumcodereview.appspot.com/23754026 missed the
case of initial-scale, so fractional values were getting clamped to
zero incorrectly.  Secondly, initial-scale values should not be clamped
in WebView.

BUG=298962,282130,295886

Review URL: https://chromiumcodereview.appspot.com/24769002

git-svn-id: svn://svn.chromium.org/blink/trunk@158476 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Add XSSInfo::isSafeToSendToAnotherThread() and call it in debug builds.

Follow-on to https://codereview.chromium.org/24816003/, adds thread-safe
checks for the XSSInfo class. Also refactors a free-standing function into a
XSSInfo method as additonal cleanup, re-arranging order of methods to match the 
header file.

BUG=299132
R=abarth@chromium.org

Review URL: https://chromiumcodereview.appspot.com/25014005

git-svn-id: svn://svn.chromium.org/blink/trunk@158477 bbb929c8-8fbe-4397-9dbb-9b2b20218538