Add multiline braille support.

chrome/common/extensions/api/braille_display_private.idl

Index: chrome/common/extensions/api/braille_display_private.idl
diff --git a/chrome/common/extensions/api/braille_display_private.idl b/chrome/common/extensions/api/braille_display_private.idl
index 0c7a3e69dc00fdbf5cb99c85ff770776dcfcb7f6..a2aa872a6fc0a747aaad459bcf0acb6b361fd262 100644
--- a/chrome/common/extensions/api/braille_display_private.idl
+++ b/chrome/common/extensions/api/braille_display_private.idl
@@ -51,8 +51,10 @@ namespace brailleDisplayPrivate {
   dictionary DisplayState {
     // Whether a braille display is currently available.
     boolean available;
-    // Number of braille cells on the currently connected display.
-    long? textCellCount;
+    // Number of rows of braille cells on the currently connected display.
+    long? textRowCount;
+    // Number of columns of braille cells on the currently connected display.
+    long? textColumnCount;
   };
 
   callback DisplayStateCallback = void(DisplayState result);
@@ -66,8 +68,12 @@ namespace brailleDisplayPrivate {
     // raised in the corresponding cell with the low-order bit representing
     // dot 1 and so on until bit 7 which corresponds to dot 8.  If the number
     // of bytes in the buffer is not equal to the display size, the buffer
-    // will either be clipped or padded with blank cells on the right.
-    static void writeDots(ArrayBuffer cells);
+    // will either be clipped or padded with blank cells on the right. The
+    // buffer is a 2D array compressed into 1D. The |columns| and |rows|
+    // parameters give the original 2D dimensions of the buffer. To access
+    // an element cells[r][c], simply access cells[r * columns + c].
+

[Devlin, 2016/10/25 22:36:54]

remove extra newline

[ultimatedbz, 2016/10/27 03:16:58]

Done.

+    static void writeDots(ArrayBuffer cells, long columns, long rows);

[David Tseng, 2016/10/26 04:49:24]

Driving by. It seems like you don't really need the rows parameter throughout
all of the bindings. The caller needs to fill the array in order to construct
the flattened cells. So, rows = ceiling(cells.size() / columns), right?

[ultimatedbz, 2016/10/27 03:16:58]

Hey David! Yes, what you said definitely makes sense and we could just derive
rows from the dividing the cell's size by |columns|. However, if we also pass in
|rows|, would you say that it makes the code more readable and clear?

[Devlin, 2016/10/27 14:59:28]

FWIW, I have a slight preference towards including both columns and rows as well
for readability.  But since its a private API, I'm fine either way.

[David Tseng, 2016/10/27 15:39:36]

As is, it is unclear what happens if you pass in less rows than is contained in
the buffer. If you mean to allow the caller to clip output, then I guess this is
fine. Otherwise, it seems unnecessary and imo unclear. 

   };
 
   interface Events {