Drop mobile memory size to 500K while SDCH is not hooked up to

MemoryPressureListener.

BUG=447208
R=ellyjones@chromium.org

Review URL: https://codereview.chromium.org/971413002

Cr-Commit-Position: refs/heads/master@{#318909}

net/sdch/sdch_owner.cc

@@ -63,7 +63,7 @@ namespace net {
 // Adjust SDCH limits downwards for mobile.
 #if defined(OS_ANDROID) || defined(OS_IOS)
 // static
-const size_t SdchOwner::kMaxTotalDictionarySize = 1000 * 1000;
+const size_t SdchOwner::kMaxTotalDictionarySize = 500 * 1000;
 #else
 // static
 const size_t SdchOwner::kMaxTotalDictionarySize = 20 * 1000 * 1000;