Add support for `width` based Width Client Hint

LayoutTests/http/tests/misc/client-hints-rw-width.html

Index: LayoutTests/http/tests/misc/client-hints-rw-width.html
diff --git a/LayoutTests/http/tests/misc/client-hints-preload-rw-sizes.html b/LayoutTests/http/tests/misc/client-hints-rw-width.html
similarity index 54%
copy from LayoutTests/http/tests/misc/client-hints-preload-rw-sizes.html
copy to LayoutTests/http/tests/misc/client-hints-rw-width.html
index f80baa6d4072390f64f95de77cd0e33c6f3edb92..a69adae856ed0e876a03f874de9a7fa05dbb761d 100644
--- a/LayoutTests/http/tests/misc/client-hints-preload-rw-sizes.html
+++ b/LayoutTests/http/tests/misc/client-hints-rw-width.html
@@ -4,16 +4,20 @@
 <script src="../resources/testharnessreport.js"></script>
 <script src="../resources/slow-script.pl?delay=300"></script>
 <img id="testimg1" src="resources/image-checks-for-width.php?rw=480" sizes="60vw">
-<img id="testimg2" sizes="40vw" src="resources/image-checks-for-width.php?rw=320" sizes="60vw">
-<img id="testimg3" sizes="50vw" src="resources/image-checks-for-width.php?rw=400">
-<img id="testimg4" sizes="50vw" src="resources/image-checks-for-viewport-width.php?viewport=800">
+<img id="testimg2" width="320" src="resources/image-checks-for-width.php?rw=320">
+<img id="testimg3" width="400bla" src="resources/image-checks-for-width.php?rw=400">
+<img id="testimg4" width="400%" src="resources/image-checks-for-width.php?bla=1">

[Mike West, 2015/06/18 06:20:03]

bla=1?

[Yoav Weiss, 2015/06/18 06:30:22]

Cache busting to avoid the same URL as "bla=2".
I can change it to foo, if preferred.

[Mike West, 2015/06/18 06:34:35]

In that case, testimg5 needs to use something other than `bla=1`. I'd suggest
`cachebust={1,2,3,...}` for clarity. :)

+<img id="testimg5" width="400%" width="400" src="resources/image-checks-for-width.php?bla=1">
+<img id="testimg6" width="400*" src="resources/image-checks-for-width.php?bla=2">

[Mike West, 2015/06/18 06:20:03]

bla=2?

 <script>
     var t = async_test('Client-Hints sent with the right Width value Accept-CH header is present');
     window.onload = t.step_func(function() {
         assert_not_equals(document.getElementById("testimg1").naturalWidth, 0);
         assert_not_equals(document.getElementById("testimg2").naturalWidth, 0);
         assert_not_equals(document.getElementById("testimg3").naturalWidth, 0);
-        assert_not_equals(document.getElementById("testimg4").naturalWidth, 0);
+        assert_equals(document.getElementById("testimg4").naturalWidth, 0);
+        assert_equals(document.getElementById("testimg5").naturalWidth, 0);
+        assert_equals(document.getElementById("testimg6").naturalWidth, 0);
         t.done();
     });
 </script>