cc: Add cache purging to software image decode controller.

cc/tiles/software_image_decode_controller.cc

Index: cc/tiles/software_image_decode_controller.cc
diff --git a/cc/tiles/software_image_decode_controller.cc b/cc/tiles/software_image_decode_controller.cc
index bca4e99010465dde00a3a517f0164d4ecdca1f33..be626eb53e490edd03f8fda131da0c912a5be9ec 100644
--- a/cc/tiles/software_image_decode_controller.cc
+++ b/cc/tiles/software_image_decode_controller.cc
@@ -37,7 +37,11 @@ const size_t kMaxHighQualityImageSizeBytes = 64 * 1024 * 1024;
 
 // The number of entries to keep around in the cache. This limit can be breached
 // if more items are locked. That is, locked items ignore this limit.
-const size_t kMaxItemsInCache = 1000;
+// Depending on the memory state of the system, we limit the amount of items
+// differently.
+const size_t kNormalMaxItemsInCache = 1000;
+const size_t kThrottledMaxItemsInCache = 100;
+const size_t kSuspendedMaxItemsInCache = 0;
 
 // If the size of the original sized image breaches kMemoryRatioToSubrect but we
 // don't need to scale the image, consider caching only the needed subrect.
@@ -173,7 +177,8 @@ SoftwareImageDecodeController::SoftwareImageDecodeController(
     : decoded_images_(ImageMRUCache::NO_AUTO_EVICT),
       at_raster_decoded_images_(ImageMRUCache::NO_AUTO_EVICT),
       locked_images_budget_(locked_memory_limit_bytes),
-      format_(format) {
+      format_(format),
+      max_items_in_cache_(kNormalMaxItemsInCache) {
   // In certain cases, ThreadTaskRunnerHandle isn't set (Android Webview).
   // Don't register a dump provider in these cases.
   if (base::ThreadTaskRunnerHandle::IsSet()) {
@@ -747,8 +752,8 @@ void SoftwareImageDecodeController::UnrefAtRasterImage(const ImageKey& key) {
 void SoftwareImageDecodeController::ReduceCacheUsage() {
   TRACE_EVENT0("cc", "SoftwareImageDecodeController::ReduceCacheUsage");
   base::AutoLock lock(lock_);
-  size_t num_to_remove = (decoded_images_.size() > kMaxItemsInCache)
-                             ? (decoded_images_.size() - kMaxItemsInCache)
+  size_t num_to_remove = (decoded_images_.size() > max_items_in_cache_)
+                             ? (decoded_images_.size() - max_items_in_cache_)
                              : 0;
   for (auto it = decoded_images_.rbegin();
        num_to_remove != 0 && it != decoded_images_.rend();) {
@@ -1085,22 +1090,24 @@ size_t SoftwareImageDecodeController::MemoryBudget::GetCurrentUsageSafe()
 
 void SoftwareImageDecodeController::OnMemoryStateChange(
     base::MemoryState state) {
-  switch (state) {
-    case base::MemoryState::NORMAL:
-      // TODO(tasak): go back to normal state.
-      break;
-    case base::MemoryState::THROTTLED:
-      // TODO(tasak): make the limits of this component's caches smaller to
-      // save memory usage.
-      break;
-    case base::MemoryState::SUSPENDED:
-      // TODO(tasak): free this component's caches as much as possible before
-      // suspending renderer.
-      break;
-    case base::MemoryState::UNKNOWN:
-      // NOT_REACHED.
-      break;
+  {
+    base::AutoLock hold(lock_);
+    switch (state) {
+      case base::MemoryState::NORMAL:
+        max_items_in_cache_ = kNormalMaxItemsInCache;
+        break;
+      case base::MemoryState::THROTTLED:
+        max_items_in_cache_ = kThrottledMaxItemsInCache;
+        break;
+      case base::MemoryState::SUSPENDED:
+        max_items_in_cache_ = kSuspendedMaxItemsInCache;
+        break;
+      case base::MemoryState::UNKNOWN:
+        NOTREACHED();
+        return;
+    }
   }
+  ReduceCacheUsage();
 }
 
 }  // namespace cc