Add DCHECK() to check ApplyStyleCommand::DoApply() to work on non-null range

third_party/WebKit/Source/core/editing/commands/ApplyStyleCommand.cpp

Index: third_party/WebKit/Source/core/editing/commands/ApplyStyleCommand.cpp
diff --git a/third_party/WebKit/Source/core/editing/commands/ApplyStyleCommand.cpp b/third_party/WebKit/Source/core/editing/commands/ApplyStyleCommand.cpp
index a3288860110bccfff73568fe04b820b379dece51..d707fdeb0f21659b9b57ad781db1e1a3865d928f 100644
--- a/third_party/WebKit/Source/core/editing/commands/ApplyStyleCommand.cpp
+++ b/third_party/WebKit/Source/core/editing/commands/ApplyStyleCommand.cpp
@@ -199,6 +199,8 @@ Position ApplyStyleCommand::EndPosition() {
 }
 
 void ApplyStyleCommand::DoApply(EditingState* editing_state) {
+  DCHECK(StartPosition().IsNotNull());
+  DCHECK(EndPosition().IsNotNull());
   switch (property_level_) {
     case kPropertyDefault: {
       // Apply the block-centric properties of the style.