Bug 1219079 - Small breakdown-related fixes for the memory tool; r=jsantell

* Add "Breakdown by" in front of dropdown selector for the selected breakdown.
* "Allocation Site" => "Allocation Stack" for breakdown's label.
* Make the coarse type breakdown bucket strings by count.

devtools/client/memory/components/toolbar.js

@@ -36,10 +36,13 @@ const Toolbar = module.exports = createClass({
       DOM.div({ className: "devtools-toolbar" }, [
         DOM.button({ className: `take-snapshot devtools-button`, onClick: onTakeSnapshotClick }),
 
-        DOM.select({
-          className: `select-breakdown`,
-          onChange: e => onBreakdownChange(e.target.value),
-        }, breakdowns.map(({ name, displayName }) => DOM.option({ value: name }, displayName))),
+        DOM.label({},
+          "Breakdown by ",
+          DOM.select({
+            className: `select-breakdown`,
+            onChange: e => onBreakdownChange(e.target.value),
+          }, breakdowns.map(({ name, displayName }) => DOM.option({ value: name }, displayName)))
+        ),
 
         DOM.label({}, [
           DOM.input({

devtools/client/memory/constants.js

@@ -49,14 +49,14 @@ const breakdowns = exports.breakdowns = {
     breakdown: {
       by: "coarseType",
       objects: ALLOCATION_STACK,
-      strings: ALLOCATION_STACK,
+      strings: COUNT,
       scripts: INTERNAL_TYPE,
       other: INTERNAL_TYPE,
     }
   },
 
   allocationStack: {
-    displayName: "Allocation Site",
+    displayName: "Allocation Stack",
     breakdown: ALLOCATION_STACK,
   },