Fixing a crash due to calling [RWHVCocoa attributedSubstringForProposedRange] when there is no focu…

content/browser/renderer_host/render_widget_host_view_mac.mm

Index: content/browser/renderer_host/render_widget_host_view_mac.mm
diff --git a/content/browser/renderer_host/render_widget_host_view_mac.mm b/content/browser/renderer_host/render_widget_host_view_mac.mm
index b67a5f3d160e4521c879bcdb7bf30b7fa005876a..d517eb53a63a0693e798c0ade244ab3231a55324 100644
--- a/content/browser/renderer_host/render_widget_host_view_mac.mm
+++ b/content/browser/renderer_host/render_widget_host_view_mac.mm
@@ -3097,7 +3097,7 @@ extern NSString *NSTextInputReplacementRangeAttributeName;
   if (!selection)
     return nil;
 
-  if (!compositionInfo->range.is_empty()) {
+  if (compositionInfo && !compositionInfo->range.is_empty()) {

[EhsanK, 2017/03/06 23:36:19]

We do get here when <input> is not focused (left some comments in the associated
bug). So in those cases this will be nullptr.

[Avi (use Gerrit), 2017/03/06 23:39:10]

Can you drop a note in the code explaining when this is null? For the next
person who runs by this... 

[EhsanK, 2017/03/07 02:48:52]

Sure. I still don't know the exact repro but I will explain the potential
scenario and bug no.

     expected_text = &markedText_;
     expected_range = compositionInfo->range;
   } else {