Web UI: Update template_expressions to handle minified Polymer 3 files

Correctly detect HTML _templates in Polymer 3 files that have been
minified (so "_template: html`<div></div>`," becomes
"_template:html`<div></div>`,").

This is necessary to correctly replace i18n template expressions for
optimized Web UIs using Polymer 3.

Bug: 965770
Change-Id: I41112d5fa437964fa079ee5cfa41115324fa2579
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1877251Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Commit-Queue: Rebekah Potter <rbpotter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#708829}

ui/base/template_expressions.cc

@@ -22,7 +22,9 @@ 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 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 };
@@ -69,14 +71,21 @@ TemplatePosition FindHtmlTemplateEnd(const base::StringPiece& source) {
 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) {
+  if (found == base::StringPiece::npos &&
+      found_min == base::StringPiece::npos) {
     out.type = NONE;
     return out;
   }
 
-  out.start = found + kHtmlTemplateStartSize;
+  out.start = found == base::StringPiece::npos
+                  ? found_min + kHtmlTemplateStartMinSize
+                  : found + kHtmlTemplateStartSize;
   TemplatePosition end = FindHtmlTemplateEnd(source.substr(out.start));
   // Template is not terminated.
   if (end.type == NONE) {

ui/base/template_expressions_unittest.cc

@@ -377,7 +377,12 @@ TEST(TemplateExpressionsTest, JSMultipleTemplates) {
        "Polymer({\n"
        "  _template: html`<div>number</div>`,\n"
        "  is: 'bar-element',\n"
-       "});"}};
+       "});"},
+      // 2 minified templates, both with substitutions.
+      {"Polymer({_template:html`<div>$i18n{test}</div>`,is:'foo-element',});\n"
+       "Polymer({_template:html`<div>$i18n{5}</div>`,is:'bar-element',});",
+       "Polymer({_template:html`<div>word</div>`,is:'foo-element',});\n"
+       "Polymer({_template:html`<div>number</div>`,is:'bar-element',});"}};
 
   std::string formatted;
   for (const TestCase test_case : kTestCases) {