Fix Find in Page on iOS 10.3.

In iOS 10.3, an error is generated when trying to find in page on a page
with iframe:

SecurityError (DOM Exception 18): Blocked a frame with origin "https://w
ww.reddit.com" from accessing a frame with origin "https://www.redditmed
ia.com". Protocols, domains, and ports must match.

As a result, the search results are not highlighted on the page.

The fix is wrapping the offending line in try/catch.

BUG=702566
TEST=On iOS 10.3 device, open cnn.com, select tools>Find in Page" and
type any string that is present on the page. The string should be found
and highglighted, and the number of results should be correct, and
next/previous buttons should scroll the page to the next/prev result.

Review-Url: https://codereview.chromium.org/2755123002
Cr-Commit-Position: refs/heads/master@{#457845}

ios/chrome/browser/find_in_page/resources/find_in_page.js

@@ -953,9 +953,21 @@ __gCrWeb['findInPage'].frameDocuments = function() {
   while (windowsToSearch.length != 0) {
     var win = windowsToSearch.pop();
     for (var i = win.frames.length - 1; i >= 0; i--) {
-      if (win.frames[i].document) {
-        documents.push(win.frames[i].document);
-        windowsToSearch.push(win.frames[i]);
+      // The following try/catch catches a webkit error when searching a page
+      // with iframes. See crbug.com/702566 for details.
+      // To verify that this is still necessary:
+      // 1. Remove this try/catch.
+      // 2. Go to a page with iframes.
+      // 3. Search for anything.
+      // 4. Check if the webkit debugger spits out SecurityError (DOM Exception)
+      // and the search fails. If it doesn't, feel free to remove this.
+      try {
+        if (win.frames[i].document) {
+          documents.push(win.frames[i].document);
+          windowsToSearch.push(win.frames[i]);
+        }
+      } catch (e) {
+        // Do nothing.
       }
     }
   }