Allow purging of asset bitmaps

Allow the system to reclaim more free RAM when needed on 'low' memory devices
(e.g. Droid/Milestone). This option enabled efectively restores the froyo
way of forcePurgeable BitmapFactory asset handling.

Change-Id: If454e92743bf91efae42a8e4bcc2d2e7f9b90e91

core/jni/android/graphics/BitmapFactory.cpp

@@ -15,6 +15,7 @@
 #include "JNIHelp.h"
 
 #include <android_runtime/AndroidRuntime.h>
+#include <cutils/properties.h>
 #include <utils/Asset.h>
 #include <utils/ResourceTypes.h>
 #include <netinet/in.h>
@@ -44,6 +45,8 @@ jfieldID gBitmap_nativeBitmapFieldID;
 
 using namespace android;
 
+bool mPurgeableAssets;
+
 static inline int32_t validOrNeg1(bool isValid, int32_t value) {
 //    return isValid ? value : -1;
     SkASSERT((int)isValid == 0 || (int)isValid == 1);
@@ -359,8 +362,8 @@ static jobject nativeDecodeAsset(JNIEnv* env, jobject clazz,
                                  jobject options) { // BitmapFactory$Options
     SkStream* stream;
     Asset* asset = reinterpret_cast<Asset*>(native_asset);
-    bool forcePurgeable = optionsPurgeable(env, options);
-    if (forcePurgeable) {
+    bool forcePurgeable = mPurgeableAssets;
+    if (forcePurgeable || optionsPurgeable(env, options)) {
         // if we could "ref/reopen" the asset, we may not need to copy it here
         // and we could assume optionsShareable, since assets are always RO
         stream = copyAssetToStream(asset);
@@ -530,6 +533,10 @@ int register_android_graphics_BitmapFactory(JNIEnv* env) {
     SkASSERT(bitmap_class);
     gBitmap_nativeBitmapFieldID = getFieldIDCheck(env, bitmap_class, "mNativeBitmap", "I");
 
+    char value[PROPERTY_VALUE_MAX];
+    property_get("persist.sys.purgeable_assets", value, "0");
+    mPurgeableAssets = atoi(value) == 1;
+
     int ret = AndroidRuntime::registerNativeMethods(env,
                                     "android/graphics/BitmapFactory$Options",
                                     gOptionsMethods,