Sync some HTML interfaces with the spec

Source/core/html/TextMetrics.idl

Index: Source/core/html/TextMetrics.idl
diff --git a/Source/core/html/TextMetrics.idl b/Source/core/html/TextMetrics.idl
index c7d929a8ffc4be0fab991ad8ea7855d688d794e6..b9bdf0644abb169a1cbfe81814e0e16588cf6a00 100644
--- a/Source/core/html/TextMetrics.idl
+++ b/Source/core/html/TextMetrics.idl
@@ -22,11 +22,16 @@
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
+
+// https://html.spec.whatwg.org/#textmetrics
+
+// TODO(philipj): All float types in this interface should be double.
 [
+    // TODO(philipj): Exposed=(Window,Worker)
     WillBeGarbageCollected,
 ] interface TextMetrics {
     // x-direction
-    readonly attribute float width;
+    readonly attribute float width; // advance width
     [RuntimeEnabled=ExperimentalCanvasFeatures] readonly attribute float actualBoundingBoxLeft;
     [RuntimeEnabled=ExperimentalCanvasFeatures] readonly attribute float actualBoundingBoxRight;