Bug 1335148 - Part 4: Remove unused max_decoded_image_kb pref. r=snorp

Since bug 1104622, that pref has in fact been unused, so us setting that value
to 0 on memory pressure didn't really achieve anything.

Instead, the SurfaceCache already does its own memory management and discards
image surfaces when receiving a memory-pressure notification.

MozReview-Commit-ID: 4aqvclgvLhX

--HG--
extra : rebase_source : c8e8970ec748ea754545e0f563d86615e220f647

browser/app/profile/firefox.js

@@ -1306,11 +1306,6 @@ pref("pdfjs.firstRun", true);
 pref("pdfjs.previousHandler.preferredAction", 0);
 pref("pdfjs.previousHandler.alwaysAskBeforeHandling", false);
 
-// The maximum amount of decoded image data we'll willingly keep around (we
-// might keep around more than this, but we'll try to get down to this value).
-// (This is intentionally on the high side; see bug 746055.)
-pref("image.mem.max_decoded_image_kb", 256000);
-
 // Is the sidebar positioned ahead of the content browser
 pref("sidebar.position_start", true);
 

mobile/android/chrome/content/MemoryObserver.js

@@ -41,9 +41,6 @@ var MemoryObserver = {
     // Change some preferences temporarily for only this session
     let defaults = Services.prefs.getDefaultBranch(null);
 
-    // Reduce the amount of decoded image data we keep around
-    defaults.setIntPref("image.mem.max_decoded_image_kb", 0);
-
     // Stop using the bfcache
     if (!Services.prefs.getBoolPref("browser.sessionhistory.bfcacheIgnoreMemoryPressure")) {
       this._defaultMaxContentViewers = defaults.getIntPref(MAX_CONTENT_VIEWERS_PREF);