Improve core/css exception messages.

Source/core/css/CSSStyleSheet.cpp

Index: Source/core/css/CSSStyleSheet.cpp
diff --git a/Source/core/css/CSSStyleSheet.cpp b/Source/core/css/CSSStyleSheet.cpp
index bc9337ec5398bab38e514ec28152e47a0ef05bbf..82b9c0ebfea1b09effefbb50652ce99d09004ebd 100644
--- a/Source/core/css/CSSStyleSheet.cpp
+++ b/Source/core/css/CSSStyleSheet.cpp
@@ -260,21 +260,21 @@ unsigned CSSStyleSheet::insertRule(const String& ruleString, unsigned index, Exc
     ASSERT(m_childRuleCSSOMWrappers.isEmpty() || m_childRuleCSSOMWrappers.size() == m_contents->ruleCount());
 
     if (index > length()) {
-        exceptionState.throwUninformativeAndGenericDOMException(IndexSizeError);
+        exceptionState.throwDOMException(IndexSizeError, "The index provided (" + String::number(index) + ") is larger than the maximum index (" + String::number(length()) + ").");
         return 0;
     }
     BisonCSSParser p(m_contents->parserContext(), UseCounter::getFrom(this));
     RefPtr<StyleRuleBase> rule = p.parseRule(m_contents.get(), ruleString);
 
     if (!rule) {
-        exceptionState.throwUninformativeAndGenericDOMException(SyntaxError);
+        exceptionState.throwDOMException(SyntaxError, "Failed to parse the rule '" + ruleString + "'.");
         return 0;
     }
     RuleMutationScope mutationScope(this);
 
     bool success = m_contents->wrapperInsertRule(rule, index);
     if (!success) {
-        exceptionState.throwUninformativeAndGenericDOMException(HierarchyRequestError);
+        exceptionState.throwDOMException(HierarchyRequestError, "Failed to insert the rule.");
         return 0;
     }
     if (!m_childRuleCSSOMWrappers.isEmpty())
@@ -294,7 +294,7 @@ void CSSStyleSheet::deleteRule(unsigned index, ExceptionState& exceptionState)
     ASSERT(m_childRuleCSSOMWrappers.isEmpty() || m_childRuleCSSOMWrappers.size() == m_contents->ruleCount());
 
     if (index >= length()) {
-        exceptionState.throwUninformativeAndGenericDOMException(IndexSizeError);
+        exceptionState.throwDOMException(IndexSizeError, "The index provided (" + String::number(index) + ") is larger than the maximum index (" + String::number(length() - 1) + ").");
         return;
     }
     RuleMutationScope mutationScope(this);