Revert 268371 "base: Increase emulated discardable memory limit."

Suspect that this is causing an increase in OOM errors.

> base: Increase emulated discardable memory limit.
>
> This increases the limit to 128MB but keeps the limit under moderate
> pressure low so the total amount of memory used by chrome is not
> significantly increased.
>
> BUG=368078
>
> Review URL: https://codereview.chromium.org/266993003

TBR=willchan@chromium.org
BUG=372158

Review URL: https://codereview.chromium.org/341773002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@278010 0039d316-1c4b-4281-b951-d872f2087c98

base/memory/discardable_memory_emulated.cc

@@ -10,10 +10,11 @@
 namespace base {
 namespace {
 
-// This is admittedly pretty magical. It's approximately enough memory for eight
+// This is admittedly pretty magical. It's approximately enough memory for four
 // 2560x1600 images.
-const size_t kEmulatedMemoryLimit = 128 * 1024 * 1024;
-const size_t kEmulatedBytesToKeepUnderModeratePressure = 12 * 1024 * 1024;
+const size_t kEmulatedMemoryLimit = 64 * 1024 * 1024;
+const size_t kEmulatedBytesToKeepUnderModeratePressure =
+    kEmulatedMemoryLimit / 4;
 
 struct SharedState {
   SharedState()