Use new is*Element() helper functions more in editing code

Source/core/editing/InsertParagraphSeparatorCommand.cpp

Index: Source/core/editing/InsertParagraphSeparatorCommand.cpp
diff --git a/Source/core/editing/InsertParagraphSeparatorCommand.cpp b/Source/core/editing/InsertParagraphSeparatorCommand.cpp
index 7f982205430f57b1261488288021694fffe2114a..417ab39e4d0bc9e65afc10d9d69080a69f7b4313 100644
--- a/Source/core/editing/InsertParagraphSeparatorCommand.cpp
+++ b/Source/core/editing/InsertParagraphSeparatorCommand.cpp
@@ -50,7 +50,7 @@ static Element* highestVisuallyEquivalentDivBelowRoot(Element* startBlock)
     Element* curBlock = startBlock;
     // We don't want to return a root node (if it happens to be a div, e.g., in a document fragment) because there are no
     // siblings for us to append to.
-    while (!curBlock->nextSibling() && curBlock->parentElement()->hasTagName(divTag) && curBlock->parentElement()->parentElement()) {
+    while (!curBlock->nextSibling() && isHTMLDivElement(*curBlock->parentElement()) && curBlock->parentElement()->parentElement()) {
         if (curBlock->parentElement()->hasAttributes())
             break;
         curBlock = curBlock->parentElement();
@@ -170,10 +170,10 @@ void InsertParagraphSeparatorCommand::doApply()
     if (!startBlock
         || !startBlock->nonShadowBoundaryParentNode()
         || isTableCell(startBlock.get())
-        || startBlock->hasTagName(formTag)
+        || isHTMLFormElement(*startBlock)
         // FIXME: If the node is hidden, we don't have a canonical position so we will do the wrong thing for tables and <hr>. https://bugs.webkit.org/show_bug.cgi?id=40342
         || (!canonicalPos.isNull() && isRenderedTable(canonicalPos.deprecatedNode()))
-        || (!canonicalPos.isNull() && canonicalPos.deprecatedNode()->hasTagName(hrTag))) {
+        || (!canonicalPos.isNull() && isHTMLHRElement(*canonicalPos.deprecatedNode()))) {
         applyCommandToComposite(InsertLineBreakCommand::create(document()));
         return;
     }
@@ -240,7 +240,7 @@ void InsertParagraphSeparatorCommand::doApply()
                 // Most of the time we want to stay at the nesting level of the startBlock (e.g., when nesting within lists). However,
                 // for div nodes, this can result in nested div tags that are hard to break out of.
                 Element* siblingNode = startBlock.get();
-                if (blockToInsert->hasTagName(divTag))
+                if (isHTMLDivElement(*blockToInsert))
                     siblingNode = highestVisuallyEquivalentDivBelowRoot(startBlock.get());
                 insertNodeAfter(blockToInsert, siblingNode);
             }