Fixing a crash due to calling [RWHVCocoa attributedSubstringForPropos…

…edRange] when there is no focused <input>.

RWHVCocoa::attributedSubstringForProposedRange maybe called when there is no
focused <input>. In such cases, renderWidgetHostView_->GetCompositionInfo() returns
nullptr.

BUG=698672

Review-Url: https://codereview.chromium.org/2732143002
Cr-Commit-Position: refs/heads/master@{#455028}
(cherry picked from commit 8c80b23)

Review-Url: https://codereview.chromium.org/2740743003 .
Cr-Commit-Position: refs/branch-heads/3029@{#65}
Cr-Branched-From: 939b32e-refs/heads/master@{#454471}

content/browser/renderer_host/render_widget_host_view_mac.mm

@@ -3097,7 +3097,10 @@ - (NSAttributedString*)attributedSubstringForProposedRange:(NSRange)range
   if (!selection)
     return nil;
 
-  if (!compositionInfo->range.is_empty()) {
+  if (compositionInfo && !compositionInfo->range.is_empty()) {
+    // This method might get called after TextInputState.type is reset to none,
+    // in which case there will be no composition range information
+    // (https://crbug.com/698672).
     expected_text = &markedText_;
     expected_range = compositionInfo->range;
   } else {