Bug 1368797 - Don't render the about:support syscall log if it doesn't exist. r=gcp

This is a Linux-specific feature and other platforms don't have it (see also
the conditional in Troubleshoot.jsm and the ifdef in aboutSupport.xhtml).

MozReview-Commit-ID: IISzOvWXwCp

--HG--
extra : rebase_source : d57c2b42003619ed13a5bb6afe219d16c5d575ae

toolkit/content/aboutSupport.js

@@ -611,8 +611,8 @@ var snapshotFormatters = {
         continue;
       }
       if (key === "syscallLog") {
-	// Not in this table.
-	continue;
+        // Not in this table.
+        continue;
       }
       tbody.appendChild($.new("tr", [
         $.new("th", strings.GetStringFromName(key), "column"),
@@ -620,25 +620,27 @@ var snapshotFormatters = {
       ]));
     }
 
-    let syscallBody = $("sandbox-syscalls-tbody");
-    let argsHead = $("sandbox-syscalls-argshead");
-    for (let syscall of data.syscallLog) {
-      if (argsHead.colSpan < syscall.args.length) {
-	argsHead.colSpan = syscall.args.length;
+    if ("syscallLog" in data) {
+      let syscallBody = $("sandbox-syscalls-tbody");
+      let argsHead = $("sandbox-syscalls-argshead");
+      for (let syscall of data.syscallLog) {
+        if (argsHead.colSpan < syscall.args.length) {
+          argsHead.colSpan = syscall.args.length;
+        }
+        let cells = [
+          $.new("td", syscall.index, "integer"),
+          $.new("td", syscall.msecAgo / 1000),
+          $.new("td", syscall.pid, "integer"),
+          $.new("td", syscall.tid, "integer"),
+          $.new("td", strings.GetStringFromName("sandboxProcType." +
+                                                syscall.procType)),
+          $.new("td", syscall.syscall, "integer"),
+        ];
+        for (let arg of syscall.args) {
+          cells.push($.new("td", arg, "integer"));
+        }
+        syscallBody.appendChild($.new("tr", cells));
       }
-      let cells = [
-	$.new("td", syscall.index, "integer"),
-	$.new("td", syscall.msecAgo / 1000),
-	$.new("td", syscall.pid, "integer"),
-	$.new("td", syscall.tid, "integer"),
-	$.new("td", strings.GetStringFromName("sandboxProcType." +
-					      syscall.procType)),
-	$.new("td", syscall.syscall, "integer"),
-      ];
-      for (let arg of syscall.args) {
-	cells.push($.new("td", arg, "integer"));
-      }
-      syscallBody.appendChild($.new("tr", cells));
     }
   },
 };