[XSS Auditor] Extract attribute truncation logic and formalize string canonicalization

[XSS Auditor] Extract attribute truncation logic and formalize string canonicalization
https://bugs.webkit.org/show_bug.cgi?id=152874

Reviewed by Brent Fulgham.

Derived from Blink patch (by Tom Sepez <tsepez@chromium.org>):
<https://src.chromium.org/viewvc/blink?revision=176339&view=revision>

Extract the src-like and script-like attribute truncation logic into independent functions
towards making it more straightforward to re-purpose this logic. Additionally, formalize the
concept of string canonicalization as a member function that consolidates the process of
decoding URL escape sequences, truncating the decoded string (if applicable), and removing
characters that are considered noise.

* html/parser/XSSAuditor.cpp:
(WebCore::truncateForSrcLikeAttribute): Extracted from XSSAuditor::decodedSnippetForAttribute().
(WebCore::truncateForScriptLikeAttribute): Ditto.
(WebCore::XSSAuditor::init): Write in terms of XSSAuditor::canonicalize().
(WebCore::XSSAuditor::filterCharacterToken): Updated to make use of formalized canonicalization methods.
(WebCore::XSSAuditor::filterScriptToken): Ditto.
(WebCore::XSSAuditor::filterObjectToken): Ditto.
(WebCore::XSSAuditor::filterParamToken): Ditto.
(WebCore::XSSAuditor::filterEmbedToken): Ditto.
(WebCore::XSSAuditor::filterAppletToken): Ditto.
(WebCore::XSSAuditor::filterFrameToken): Ditto.
(WebCore::XSSAuditor::filterInputToken): Ditto.
(WebCore::XSSAuditor::filterButtonToken): Ditto.
(WebCore::XSSAuditor::eraseDangerousAttributesIfInjected): Ditto.
(WebCore::XSSAuditor::eraseAttributeIfInjected): Updated code to use early return style and avoid an unnecessary string
comparison when we know that a src attribute was injected.
(WebCore::XSSAuditor::canonicalizedSnippetForTagName): Renamed; formerly known as XSSAuditor::decodedSnippetForName(). Updated
to make use of XSSAuditor::canonicalize().
(WebCore::XSSAuditor::snippetFromAttribute): Renamed; formerly known as XSSAuditor::decodedSnippetForAttribute(). Moved
truncation logic from here to WebCore::truncateFor{Script, Src}LikeAttribute.
(WebCore::XSSAuditor::canonicalize): Added.
(WebCore::XSSAuditor::canonicalizedSnippetForJavaScript): Added.
(WebCore::canonicalize): Deleted.
(WebCore::XSSAuditor::decodedSnippetForName): Deleted.
(WebCore::XSSAuditor::decodedSnippetForAttribute): Deleted.
(WebCore::XSSAuditor::decodedSnippetForJavaScript): Deleted.
* html/parser/XSSAuditor.h: Define enum class for the various attribute truncation styles.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@195074 268f45cc-cd09-0410-ab3c-d52691b4dbfc