Remove useless calls to v8::Value::ToString()

Remove useless calls to v8::Value::ToString() after we already checked
that v8::Value::IsString() already returns true. Use
v8::Handle::As<v8::String>() instead, which is more efficient as it
does not call v8::Value::IsString() again.

R=haraken
BUG=

Review URL: https://chromiumcodereview.appspot.com/23578025

git-svn-id: svn://svn.chromium.org/blink/trunk@157678 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Expose navigator.product and navigator.appCodeName constants to workers

Expose navigator.product and navigator.appCodeName constants to web workers as
well, as per the specification:
http://www.whatwg.org/specs/web-apps/current-work/multipage/workers.html#workernavigator
http://www.whatwg.org/specs/web-apps/current-work/multipage/timers.html#navigatorid

BUG=276316

Review URL: https://chromiumcodereview.appspot.com/22866014

git-svn-id: svn://svn.chromium.org/blink/trunk@157679 bbb929c8-8fbe-4397-9dbb-9b2b20218538
HeapProfiler: Show string content as node name for concatenated strings.

ConsString is not a string from internal point of view.
But users would like to see the content of these strings.
So we reconstructs the content of these strings lazily.

The binary tree of the ConsStrings could be very deep
so we can't use the recursion here.

BUG=none

Review URL: https://chromiumcodereview.appspot.com/23868019

git-svn-id: svn://svn.chromium.org/blink/trunk@157680 bbb929c8-8fbe-4397-9dbb-9b2b20218538