[autofill] Fix --show-autofill-type-predictions.

Corrects the code that generates field title strings when the
--show-autofill-type-predictions flag is specified. Formatting
bugs were introduced when the string was moved out of the .pak
file and into code (escape sequences for string replacement
were retained and some values were duplicated/missing due to
copy-paste).

BUG=703134

Change-Id: Id81a974be4ee12f0c6e2870da2b80c592962d730
Reviewed-on: https://chromium-review.googlesource.com/600994
Commit-Queue: Roger McFarlane <rogerm@chromium.org>
Reviewed-by: Mathieu Perreault <mathp@chromium.org>
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/master@{#491852}

components/autofill/content/renderer/form_cache.cc

@@ -310,27 +310,36 @@ bool FormCache::ShowPredictions(const FormDataPredictions& form) {
       continue;
     }
 
-    static const size_t kMaxLabelSize = 100;
+    constexpr size_t kMaxLabelSize = 100;
     const base::string16 truncated_label = field_data.label.substr(
         0, std::min(field_data.label.length(), kMaxLabelSize));
 
     const FormFieldDataPredictions& field = form.fields[i];
 
+    // A rough estimate of the maximum title size is:
+    //    7 field titles at <17 chars each
+    //    + 6 values at <40 chars each
+    //    + 1 truncated label at <kMaxLabelSize;
+    //    = 459 chars, rounded up to the next multiple of 64 = 512
+    // A particularly large parseable name could blow through this and cause
+    // another allocation, but that's OK.
+    constexpr size_t kMaxTitleSize = 512;
     std::string title;
+    title.reserve(kMaxTitleSize);
     title += "overall type: ";
     title += field.overall_type;
-    title += " server type: $2 ";
+    title += "\nserver type: ";
     title += field.server_type;
-    title += " heuristic type: $3";
+    title += "\nheuristic type: ";
     title += field.heuristic_type;
-    title += " label: $4";
+    title += "\nlabel: ";
     title += base::UTF16ToUTF8(truncated_label);
-    title += " parseable name: $5";
-    title += field.overall_type;
-    title += " field signature: $6";
-    title += field.overall_type;
-    title += " form signature: $7";
-    title += field.overall_type;
+    title += "\nparseable name: ";
+    title += field.parseable_name;
+    title += "\nfield signature: ";
+    title += field.signature;
+    title += "\nform signature: ";
+    title += form.signature;
 
     element.SetAttribute("title", WebString::FromUTF8(title));