Web UI: Update template_expressions.cc to use new start/end markers

Update template expressions replacement to use the new HTML template
start and end markers instead of looking for _template: html` and `,.
This allows some simplification of the logic and will enable i18n
replacements in JS files using class based Polymer 3 syntax, since
the autogeneration code adds these markers to the start and end of
HTML templates at build time regardless of syntax.

Also modifying some existing tests to use class based syntax, and
adding more tests for less common cases and for mixed class/legacy
syntax.

Bug: 1023841
Change-Id: I764ee18621bc526f259b7b970e6008e0de220711
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1935609Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Commit-Queue: Rebekah Potter <rbpotter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#719259}

ui/base/template_expressions.cc

@@ -21,18 +21,11 @@ const char kLeader[] = "$i18n";
 const size_t kLeaderSize = base::size(kLeader) - 1;
 const char kKeyOpen = '{';
 const char kKeyClose = '}';
-const char kHtmlTemplateStart[] = "_template: html`";
-const char kHtmlTemplateStartMin[] = "_template:html`";
+const char kHtmlTemplateEnd[] = "<!--_html_template_end_-->";
+const char kHtmlTemplateStart[] = "<!--_html_template_start_-->";
 const size_t kHtmlTemplateStartSize = base::size(kHtmlTemplateStart) - 1;
-const size_t kHtmlTemplateStartMinSize = base::size(kHtmlTemplateStartMin) - 1;
 
-// Currently only legacy _template: html`...`, syntax is supported.
-enum HtmlTemplateType { INVALID = 0, NONE = 1, LEGACY = 2 };
-
-struct TemplatePosition {
-  HtmlTemplateType type;
-  base::StringPiece::size_type position;
-};
+enum HtmlTemplateType { INVALID = 0, NONE = 1, VALID = 2 };
 
 struct HtmlTemplate {
   base::StringPiece::size_type start;
@@ -40,60 +33,26 @@ struct HtmlTemplate {
   HtmlTemplateType type;
 };
 
-TemplatePosition FindHtmlTemplateEnd(const base::StringPiece& source) {
-  enum State { OPEN, IN_ESCAPE, IN_TICK };
-  State state = OPEN;
-
-  for (base::StringPiece::size_type i = 0; i < source.length(); i++) {
-    if (state == IN_ESCAPE) {
-      state = OPEN;  // Consume
-      continue;
-    }
-
-    switch (source[i]) {
-      case '\\':
-        state = IN_ESCAPE;
-        break;
-      case '`':
-        state = IN_TICK;
-        break;
-      case ',':
-        if (state == IN_TICK)
-          return {LEGACY, i - 1};
-        FALLTHROUGH;
-      default:
-        state = OPEN;
-    }
-  }
-  return {NONE, base::StringPiece::npos};
-}
-
 HtmlTemplate FindHtmlTemplate(const base::StringPiece& source) {
   HtmlTemplate out;
   base::StringPiece::size_type found = source.find(kHtmlTemplateStart);
-  base::StringPiece::size_type found_min = base::StringPiece::npos;
-  if (found == base::StringPiece::npos) {
-    found_min = source.find(kHtmlTemplateStartMin);
-  }
 
   // No template found, return early.
-  if (found == base::StringPiece::npos &&
-      found_min == base::StringPiece::npos) {
+  if (found == base::StringPiece::npos) {
     out.type = NONE;
     return out;
   }
 
-  out.start = found == base::StringPiece::npos
-                  ? found_min + kHtmlTemplateStartMinSize
-                  : found + kHtmlTemplateStartSize;
-  TemplatePosition end = FindHtmlTemplateEnd(source.substr(out.start));
+  out.start = found + kHtmlTemplateStartSize;
+  base::StringPiece::size_type found_end =
+      source.find(kHtmlTemplateEnd, out.start);
   // Template is not terminated.
-  if (end.type == NONE) {
+  if (found_end == base::StringPiece::npos) {
     out.type = INVALID;
     return out;
   }
 
-  out.length = end.position;
+  out.length = found_end - out.start;
   // Check for a nested template
   if (source.substr(out.start, out.length).find(kHtmlTemplateStart) !=
       base::StringPiece::npos) {
@@ -101,7 +60,7 @@ HtmlTemplate FindHtmlTemplate(const base::StringPiece& source) {
     return out;
   }
 
-  out.type = LEGACY;
+  out.type = VALID;
   return out;
 }