DevTools: do not use range indices outside of InspectorStyleSheet.

LayoutTests/inspector-protocol/css/css-set-rule-selector-expected.txt

 ==== Initial style sheet text ====
 * {
     box-sizing: border-box;
 }
 
 html, body, div, a {
     /* resetting some properties */
     padding: 0;
     margin: 0;
     border: 0;
@@ skipping 82 matching lines @@
     display: flex; /* flex FTW! */
 }
 
 .EDITED { font-size: 200%; } .EDITED-2 {
     position: relative;
 }
 
 
 
 Running test: testInvalidSelectorText
-Expected protocol error: SyntaxError Selector text is not valid.
+Expected protocol error: SyntaxError Selector or media text is not valid.
 
 Running test: testEmptySelector
-Expected protocol error: SyntaxError Selector text is not valid.
+Expected protocol error: SyntaxError Selector or media text is not valid.
 
 Running test: testSelectorTextWithUnclosedComment
-Expected protocol error: SyntaxError Selector text is not valid.
+Expected protocol error: SyntaxError Selector or media text is not valid.
 
 Running test: testEditSubSelector
-Expected protocol error: Source range didn't match any rule selector source range
+Expected protocol error: NotFoundError Source range didn't match existing source range
 
 Running test: testInvalidParameters
 Expected protocol error: range.startLine must be a non-negative integer
 
 Running test: testNegativeRangeParameters
 Expected protocol error: range.startLine must be a non-negative integer
 
 Running test: testStartLineOutOfBounds
 Expected protocol error: Specified range is out of bounds
 
 Running test: testEndLineOutOfBounds
 Expected protocol error: Specified range is out of bounds
 
 Running test: testStartColumnBeyondLastLineCharacter
 Expected protocol error: Specified range is out of bounds
 
 Running test: testEndColumnBeyondLastLineCharacter
 Expected protocol error: Specified range is out of bounds
 
 Running test: testInsertBeyondLastCharacterOfLastLine
 Expected protocol error: Specified range is out of bounds
 
 Running test: testReversedRange
 Expected protocol error: Range start must not succeed its end