Remove uses of base::hash_map from //chrome

chrome/browser/chromeos/input_method/input_method_util.cc

Index: chrome/browser/chromeos/input_method/input_method_util.cc
diff --git a/chrome/browser/chromeos/input_method/input_method_util.cc b/chrome/browser/chromeos/input_method/input_method_util.cc
index 48085cf98931c9485e74505234aaba3fa7736df7..89ef419cfcb8d1a7f02d7181638ab985237c04a4 100644
--- a/chrome/browser/chromeos/input_method/input_method_util.cc
+++ b/chrome/browser/chromeos/input_method/input_method_util.cc
@@ -379,13 +379,20 @@ InputMethodUtil::InputMethodUtil(InputMethodDelegate* delegate)
   ResetInputMethods(default_input_methods);
 
   // Initialize a map from English string to Chrome string resource ID as well.
+  // Since this array is write-once, initialize a flat map in one step with a
+  // given vector storage.
+  std::vector<EnglishToIDMap::value_type> map_storage;
+  map_storage.reserve(kEnglishToResourceIdArraySize);
   for (size_t i = 0; i < kEnglishToResourceIdArraySize; ++i) {
     const EnglishToResouceId& map_entry = kEnglishToResourceIdArray[i];
-    const bool result = english_to_resource_id_.insert(std::make_pair(
-        map_entry.english_string_from_ibus, map_entry.resource_id)).second;
-    DCHECK(result) << "Duplicated string is found: "
-                   << map_entry.english_string_from_ibus;
+    map_storage.emplace_back(map_entry.english_string_from_ibus,
+                             map_entry.resource_id);

[chrisha, 2017/05/23 20:07:59]

nit: Instead of dynamically creating a const flat_map here, can't we simply
search through the already ordered static array?

(This isn't a huge absolute cost, but duplicating memory for no reason is
wasteful. If only we also had a way to check and enforce the no-dupes and sorted
requirements at compile time...)

[brettw, 2017/06/28 23:58:39]

That would be better but I just spent 2 hours on the downloads one. I don't
think this (which I'm not even set up to test locally) would be a good use of my
time.

   }
+
+  english_to_resource_id_ =
+      EnglishToIDMap(std::move(map_storage), base::KEEP_FIRST_OF_DUPES);
+  DCHECK(english_to_resource_id_.size() == kEnglishToResourceIdArraySize)
+      << "Duplicate string is found";
 }
 
 InputMethodUtil::~InputMethodUtil() {
@@ -415,7 +422,7 @@ bool InputMethodUtil::TranslateStringInternal(
   // to get the translated string.
   std::string key_string = extension_ime_util::MaybeGetLegacyXkbId(
       english_string);
-  HashType::const_iterator iter = english_to_resource_id_.find(key_string);
+  auto iter = english_to_resource_id_.find(key_string);

[chrisha, 2017/05/23 20:07:59]

Just use std::binary_search?

 
   if (iter == english_to_resource_id_.end()) {
     // TODO(yusukes): Write Autotest which checks if all display names and all