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

content/browser/renderer_host/render_widget_host_view_mac.mm

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/renderer_host/render_widget_host_view_mac.h"
 
 #import <Carbon/Carbon.h>
 #import <objc/runtime.h>
 #include <OpenGL/gl.h>
 #include <QuartzCore/QuartzCore.h>
@@ skipping 3079 matching lines @@
 
   gfx::Range expected_range;
   const base::string16* expected_text;
   const content::TextInputManager::CompositionRangeInfo* compositionInfo =
       renderWidgetHostView_->GetCompositionRangeInfo();
   const content::TextInputManager::TextSelection* selection =
       renderWidgetHostView_->GetTextSelection();
   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 {
     expected_text = &selection->text();
     size_t offset = selection->offset();
     expected_range = gfx::Range(offset, offset + expected_text->size());
   }
 
   gfx::Range actual_range = expected_range.Intersect(requested_range);
   if (!actual_range.IsValid())
@@ skipping 378 matching lines @@
 
 // "-webkit-app-region: drag | no-drag" is implemented on Mac by excluding
 // regions that are not draggable. (See ControlRegionView in
 // native_app_window_cocoa.mm). This requires the render host view to be
 // draggable by default.
 - (BOOL)mouseDownCanMoveWindow {
   return YES;
 }
 
 @end