android: add ThumbnailCache

chrome/browser/android/thumbnail/thumbnail_cache.cc

Index: chrome/browser/android/thumbnail/thumbnail_cache.cc
diff --git a/chrome/browser/android/thumbnail/thumbnail_cache.cc b/chrome/browser/android/thumbnail/thumbnail_cache.cc
new file mode 100644
index 0000000000000000000000000000000000000000..7156e800bbab4d996567602ce8f38ed720fe55e4
--- /dev/null
+++ b/chrome/browser/android/thumbnail/thumbnail_cache.cc
@@ -0,0 +1,660 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chrome/browser/android/thumbnail/thumbnail_cache.h"
+
+#include <algorithm>
+#include <cmath>
+
+#include "base/file_util.h"
+#include "base/files/file.h"
+#include "base/files/file_enumerator.h"
+#include "base/files/file_path.h"
+#include "base/strings/string_number_conversions.h"
+#include "base/time/time.h"
+#include "content/public/browser/android/ui_resource_provider.h"
+#include "content/public/browser/browser_thread.h"
+#include "third_party/android_opengl/etc1/etc1.h"
+#include "third_party/skia/include/core/SkBitmap.h"
+#include "third_party/skia/include/core/SkCanvas.h"
+#include "third_party/skia/include/core/SkData.h"
+#include "third_party/skia/include/core/SkMallocPixelRef.h"
+#include "third_party/skia/include/core/SkPixelRef.h"
+#include "ui/gfx/geometry/size_conversions.h"
+
+namespace {
+
+const float kApproximationScaleFactor = 4.f;
+const base::TimeDelta kCaptureMinRequestTimeMs(
+    base::TimeDelta::FromMilliseconds(1000));
+const Thumbnail kInvalidThumbnail;
+
+const int kCompressedKey = 0xABABABAB;
+const int kDecompressedKey = 0xCDCDCDCD;
+
+// ETC1 texture sizes are multiples of four.
+size_t NextETC1Size(size_t s) {
+  return (s / 4 + (s % 4 ? 1 : 0)) * 4;
+}
+
+gfx::Size GetEncodedSize(const gfx::Size& bitmap_size) {
+  return gfx::Size(NextETC1Size(bitmap_size.width()),
+                   NextETC1Size(bitmap_size.height()));
+}
+
+}  // anonymous namespace
+
+ThumbnailCache::ThumbnailCache(const std::string& disk_cache_path_str,
+                               size_t default_cache_size,
+                               size_t approximation_cache_size,
+                               size_t compression_queue_max_size,
+                               size_t write_queue_max_size,
+                               bool use_approximation_thumbnail)
+    : disk_cache_path_(disk_cache_path_str),
+      compression_queue_max_size_(compression_queue_max_size),
+      write_queue_max_size_(write_queue_max_size),
+      use_approximation_thumbnail_(use_approximation_thumbnail),
+      compression_tasks_count_(0),
+      write_tasks_count_(0),
+      cache_(default_cache_size),
+      approximation_cache_(approximation_cache_size),
+      ui_resource_provider_(NULL),
+      compression_thread_("thumbnail_compression"),
+      weak_factory_(this) {
+  compression_thread_.Start();
+}
+
+ThumbnailCache::~ThumbnailCache() {
+  compression_thread_.Stop();
+  SetUIResourceProvider(NULL);
+}
+
+void ThumbnailCache::SetUIResourceProvider(
+    content::UIResourceProvider* ui_resource_provider) {
+  if (ui_resource_provider_ == ui_resource_provider)
+    return;
+
+  approximation_cache_.Clear();
+  cache_.Clear();
+
+  ui_resource_provider_ = ui_resource_provider;
+}
+
+void ThumbnailCache::AddThumbnailCacheObserver(
+    ThumbnailCacheObserver* observer) {
+  if (!observers_.HasObserver(observer))
+    observers_.AddObserver(observer);
+}
+
+void ThumbnailCache::RemoveThumbnailCacheObserver(
+    ThumbnailCacheObserver* observer) {
+  if (observers_.HasObserver(observer))
+    observers_.RemoveObserver(observer);
+}
+
+void ThumbnailCache::Put(TabId tab_id,
+                         const SkBitmap& bitmap,
+                         float thumbnail_scale) {
+  if (!ui_resource_provider_ || bitmap.empty() || thumbnail_scale <= 0)
+    return;
+
+  DCHECK(thumbnail_meta_data_.find(tab_id) != thumbnail_meta_data_.end());
+
+  base::Time time_stamp = thumbnail_meta_data_[tab_id].capture_time();
+
+  Thumbnail thumbnail(
+      tab_id, time_stamp, thumbnail_scale, ui_resource_provider_, this);
+  thumbnail.SetBitmap(bitmap);
+
+  RemoveFromReadQueue(tab_id);
+  MakeSpaceForNewItemIfNecessary(tab_id);
+  cache_.Put(tab_id, thumbnail);

[David Trainor- moved to gerrit, 2014/07/14 20:30:46]

I'm not a huge fan of using references instead of pointers since if you/someone
else decided to touch thumbnail after this line it would be acting on a
different instance of the object.  thumbnail will be destroyed when this
function leaves scope.

[powei, 2014/07/15 20:06:09]

Done.  Note that lru_expiring_cache is now scoped_ptr_expiring_cache

+
+  if (use_approximation_thumbnail_) {
+    std::pair<SkBitmap, float> approximation =
+        CreateApproximation(bitmap, thumbnail_scale);
+    Thumbnail approx_thumbnail(tab_id,
+                               time_stamp,
+                               approximation.second,
+                               ui_resource_provider_,
+                               this);
+    approx_thumbnail.SetBitmap(approximation.first);
+    approximation_cache_.Put(tab_id, approx_thumbnail);
+  }
+  CompressThumbnailIfNecessary(tab_id, bitmap, thumbnail_scale, time_stamp);
+}
+
+void ThumbnailCache::Remove(TabId tab_id) {
+  cache_.Remove(tab_id);
+  approximation_cache_.Remove(tab_id);
+  thumbnail_meta_data_.erase(tab_id);
+  RemoveFromDisk(tab_id);
+  RemoveFromReadQueue(tab_id);
+}
+
+const Thumbnail& ThumbnailCache::Get(TabId tab_id) {

[David Trainor- moved to gerrit, 2014/07/14 20:30:46]

This feels a bit heavyweight, as in someone has to check if the thumbnail exists
before calling Get even though NULL is expected for some tabs.  Can this return
a pointer/NULL instead?

[powei, 2014/07/15 20:06:09]

Done.

+  if (cache_.Contains(tab_id)) {
+    Thumbnail& thumbnail = cache_.Get(tab_id);
+    thumbnail.CreateUIResource();
+    return thumbnail;
+  }
+
+  if (written_thumbnails_.find(tab_id) != written_thumbnails_.end() &&

[David Trainor- moved to gerrit, 2014/07/14 20:30:46]

written_thumbnails_ won't be up to date if we restart.  Do we need this
variable?

[powei, 2014/07/14 23:56:25]

This use to fallback to just checking the disk, but that created a pretty
noticeable regression.  Maybe we can check the disk on ThumbnailCache creation
to keep written_thumbnails_ update to date?

[powei, 2014/07/15 20:06:09]

|written_thumbnails_| is a misnomer.  It's more like a subset of the written
thumbnails.  If a thumbnail is not in this subset, then we do not want to
schedule a read for that thumbnail here (but it might later be read in
UpdateVisibleIds).  Renamed to |written_thumbnails_subset_| for now.

[David Trainor- moved to gerrit, 2014/07/15 20:08:24]

What kind of regression?  Couldn't the read task just return null if the file
didn't exist and we just don't add the thumbnail?  This seemed to work fine in
the Java version I'd almost not rather try to keep another list in sync.  If
it's a significant regression we probably also don't want to delay startup time.

[powei, 2014/07/18 00:51:49]

Currently we ask for the *static page* (i.e. thumbnail) even when only the live
page is visible.  

The java code had a flag that only goes to disk when that flag is true.  I've
added that flag back in and removed this |written_thumbnails_|

+      std::find(visible_ids_.begin(), visible_ids_.end(), tab_id) !=
+          visible_ids_.end() &&
+      std::find(read_queue_.begin(), read_queue_.end(), tab_id) ==
+          read_queue_.end()) {
+    read_queue_.push_back(tab_id);
+    ReadNextThumbnail();
+  }
+
+  if (approximation_cache_.Contains(tab_id)) {
+    Thumbnail& thumbnail = approximation_cache_.Get(tab_id);
+    thumbnail.CreateUIResource();
+    return thumbnail;
+  }
+
+  return kInvalidThumbnail;
+}
+
+void ThumbnailCache::RemoveFromDiskAtAndAboveId(TabId min_id) {
+  base::Closure remove_task =
+      base::Bind(&ThumbnailCache::RemoveFromDiskAtAndAboveIdTask,
+                 disk_cache_path_,
+                 min_id);
+  content::BrowserThread::PostTask(
+      content::BrowserThread::FILE, FROM_HERE, remove_task);
+}
+
+void ThumbnailCache::InvalidateThumbnailIfChanged(TabId tab_id,
+                                                  const GURL& url) {
+  ThumbnailMetaDataMap::iterator meta_data_iter =
+      thumbnail_meta_data_.find(tab_id);
+  if (meta_data_iter == thumbnail_meta_data_.end()) {
+    thumbnail_meta_data_[tab_id] = ThumbnailMetaData(base::Time(), url);
+  } else if (meta_data_iter->second.url() != url) {
+    Remove(tab_id);
+  }
+}
+
+bool ThumbnailCache::CheckAndUpdateThumbnailMetaData(TabId tab_id,
+                                                     const GURL& url) {
+  base::Time current_time = base::Time::Now();
+  ThumbnailMetaDataMap::iterator meta_data_iter =
+      thumbnail_meta_data_.find(tab_id);
+  if (meta_data_iter != thumbnail_meta_data_.end() &&
+      meta_data_iter->second.url() == url &&
+      (current_time - meta_data_iter->second.capture_time()) <
+          kCaptureMinRequestTimeMs) {
+    return false;
+  }
+
+  thumbnail_meta_data_[tab_id] = ThumbnailMetaData(current_time, url);
+  return true;
+}
+
+void ThumbnailCache::UpdateVisibleIds(const TabIdList& priority) {
+  if (priority.empty()) {
+    visible_ids_.clear();
+    return;
+  }
+
+  size_t ids_size = std::min(priority.size(), cache_.MaximumCacheSize());
+  if (visible_ids_.size() == ids_size) {
+    // Early out if called with the same input as last time (We only care
+    // about the first mCache.MaximumCacheSize() entries).
+    bool lists_differ = false;
+    TabIdList::const_iterator visible_iter = visible_ids_.begin();
+    TabIdList::const_iterator priority_iter = priority.begin();
+    while (visible_iter != visible_ids_.end() &&
+           priority_iter != priority.end()) {
+      if (*priority_iter != *visible_iter) {
+        lists_differ = true;
+        break;
+      }
+      visible_iter++;
+      priority_iter++;
+    }
+
+    if (!lists_differ)
+      return;
+  }
+
+  read_queue_.clear();
+  visible_ids_.clear();
+  size_t count = 0;
+  TabIdList::const_iterator iter = priority.begin();
+  while (iter != priority.end() && count < ids_size) {
+    TabId tab_id = *iter;
+    visible_ids_.push_back(tab_id);
+    if (!cache_.Contains(tab_id) &&
+        std::find(read_queue_.begin(), read_queue_.end(), tab_id) ==
+            read_queue_.end()) {
+      read_queue_.push_back(tab_id);
+    }
+    iter++;
+    count++;
+  }
+
+  ReadNextThumbnail();
+}
+
+void ThumbnailCache::RemoveFromDisk(TabId tab_id) {
+  if (written_thumbnails_.find(tab_id) == written_thumbnails_.end())
+    return;
+
+  written_thumbnails_.erase(tab_id);
+
+  base::FilePath file_path = GetFilePath(tab_id);
+  base::Closure task =
+      base::Bind(&ThumbnailCache::RemoveFromDiskTask, file_path);
+  content::BrowserThread::PostTask(
+      content::BrowserThread::FILE, FROM_HERE, task);
+}
+
+void ThumbnailCache::RemoveFromDiskTask(const base::FilePath& file_path) {
+  DCHECK(base::PathExists(file_path));
+  base::DeleteFile(file_path, false);
+}
+
+void ThumbnailCache::RemoveFromDiskAtAndAboveIdTask(
+    const base::FilePath& dir_path,
+    TabId min_id) {
+  base::FileEnumerator enumerator(dir_path, false, base::FileEnumerator::FILES);
+  while (true) {
+    base::FilePath path = enumerator.Next();
+    if (path.empty())
+      break;
+    base::FileEnumerator::FileInfo info = enumerator.GetInfo();
+    TabId tab_id;
+    bool success = base::StringToInt(info.GetName().value(), &tab_id);
+    if (success && tab_id >= min_id)
+      base::DeleteFile(path, false);
+  }
+}
+
+void ThumbnailCache::WriteThumbnailIfNecessary(
+    TabId tab_id,
+    skia::RefPtr<SkPixelRef> compressed_data,
+    float scale,
+    const gfx::Size& content_size) {
+  if (write_tasks_count_ >= write_queue_max_size_)

[David Trainor- moved to gerrit, 2014/07/14 20:30:46]

What do we do if we're over this limit?  Do we just never write it?

[powei, 2014/07/14 23:56:25]

Yes, it is just never written.  Maybe we'll need to drop the thumbnail like with
compression?

[powei, 2014/07/15 20:06:09]

Actually, I think we can live with not writing it and just have the compressed
version, which should be in |cache_|.

[David Trainor- moved to gerrit, 2014/07/15 20:08:23]

Do these max write queue/compress queue checks do anything useful?  I wonder if
the code to track how often to grab a thumbnail bitmap end up being enough and
we can remove these.  Could you do some tests to see if we can hit these?

[powei, 2014/07/18 00:51:49]

I did some manual testing.  We do hit the compression check
(compression_queue_max_size_ == 5 for the debug build).  And since the write
happens only after compression and write seems faster, I've never seen this
write check getting hit.

[David Trainor- moved to gerrit, 2014/07/18 17:03:59]

Oh interesting... if we're peaked out in the compression list we should probably
drop the texture altogether so we don't just sit with the uncompressed version
forever... I'm a bit surprised we hit it.  We shouldn't be grabbing a thumbnail
if we don't really have anything to show (and I can't really imagine us having
stuff to show  if we're swapping that fast).  That was probably a bug in the old
version too.

+    return;
+
+  write_tasks_count_++;
+
+  scoped_refptr<WriteTaskResult> result =
+      make_scoped_refptr(new WriteTaskResult());
+  base::Closure write_task = base::Bind(&ThumbnailCache::WriteTask,
+                                        GetFilePath(tab_id),
+                                        compressed_data,

[David Trainor- moved to gerrit, 2014/07/14 20:30:46]

Huh is skia::RefPtr<> thread safe?  I just realized from looking at your
CompressedDataTransport

[powei, 2014/07/14 23:56:25]

SkRefCnt does use atomic operations and barrier for thread safety.
https://cs.corp.google.com/#clankium/src/third_party/skia/include/core/SkRefC...

[David Trainor- moved to gerrit, 2014/07/18 17:03:59]

w00t

+                                        scale,
+                                        content_size,
+                                        result);
+  base::Closure post_write_task = base::Bind(&ThumbnailCache::PostWriteTask,
+                                             weak_factory_.GetWeakPtr(),
+                                             tab_id,
+                                             result);
+
+  content::BrowserThread::PostTaskAndReply(
+      content::BrowserThread::FILE, FROM_HERE, write_task, post_write_task);
+}
+
+void ThumbnailCache::CompressThumbnailIfNecessary(TabId tab_id,
+                                                  const SkBitmap& bitmap,
+                                                  float scale,
+                                                  base::Time& time_stamp) {
+  if (compression_tasks_count_ >= compression_queue_max_size_)

[David Trainor- moved to gerrit, 2014/07/14 20:30:46]

What do we do if we're over this limit?  If we just return here we won't
write/compress the data ever right?  Should we just drop the thumbnail
completely?  What do you think we should do?

[powei, 2014/07/14 23:56:25]

Yeah, maybe we'll need to drop if the approximated version is not desirable.

[powei, 2014/07/15 20:06:09]

Done.  Added line to remove the cached version.

[David Trainor- moved to gerrit, 2014/07/15 20:08:23]

Yeah that makes sense :)

+    return;
+
+  compression_tasks_count_++;
+
+  scoped_refptr<CompressedDataTransport> transport =
+      make_scoped_refptr(new CompressedDataTransport());
+  base::Closure compression_task =
+      base::Bind(&ThumbnailCache::CompressionTask, bitmap, transport);
+  base::Closure post_compression_task =
+      base::Bind(&ThumbnailCache::PostCompressionTask,
+                 weak_factory_.GetWeakPtr(),
+                 tab_id,
+                 scale,
+                 time_stamp,
+                 transport);

[David Trainor- moved to gerrit, 2014/07/14 20:30:46]

Is this the only way to do this?  Do you need to know all the parameters when
calling back to the reply?  That seems odd (or not, I don't really now the APIs
for this base::Closure).  I wonder if you need to create this object here.

[powei, 2014/07/14 23:56:25]

Closure should have no unbound parameters
(https://code.google.com/p/chromium/codesearch#chromium/src/base/callback.h).  
And PostTaskAndReply takes reply as a closure.

[David Trainor- moved to gerrit, 2014/07/15 20:08:24]

Do you have to use PostTaskAndReply?  Would it be cleaner to have the task post
another task back to the UI thread when it's done with the right arguments?

[powei, 2014/07/18 00:51:49]

Done.  Pass the Post*Task() as callback params to to *Task() methods.

+
+  DCHECK(compression_thread_.message_loop_proxy());
+  compression_thread_.message_loop_proxy()->PostTaskAndReply(
+      FROM_HERE, compression_task, post_compression_task);
+}
+
+void ThumbnailCache::ReadNextThumbnail() {
+  if (read_queue_.empty())

[David Trainor- moved to gerrit, 2014/07/15 20:08:24]

I'm still a bit confused by this queue :(.  It might/might not actually
represent what's queued up to be read (we could have 4-5 tasks posted to the io
thread depending on how you call certain methods... which means this queue might
not actually represent what's happening).  That means you could in theory read
in the same tab a bunch of times right?

[powei, 2014/07/18 00:51:49]

I added a boolean to indicate that a read is currently being carried out.  So
only one read should be in flight at any time.

The read queue is not dequeued until the read is finished (PostReadTask), and
there are checks to ensure the queue does not contain duplicates.  So after
adding the above bool flag, we won't see multiple reads for the same tab in the
queue.  

+    return;
+
+  TabId tab_id = read_queue_.front();
+
+  scoped_refptr<CompressedDataTransport> transport =
+      make_scoped_refptr(new CompressedDataTransport());
+  base::FilePath file_path = GetFilePath(tab_id);
+  base::Closure read_task =
+      base::Bind(&ThumbnailCache::ReadTask, file_path, transport);
+  base::Closure post_read_task = base::Bind(&ThumbnailCache::PostReadTask,
+                                            weak_factory_.GetWeakPtr(),
+                                            tab_id,
+                                            transport);
+
+  content::BrowserThread::PostTaskAndReply(
+      content::BrowserThread::FILE, FROM_HERE, read_task, post_read_task);
+}
+
+void ThumbnailCache::MakeSpaceForNewItemIfNecessary(TabId tab_id) {
+  if (cache_.Contains(tab_id) ||
+      std::find(visible_ids_.begin(), visible_ids_.end(), tab_id) ==
+          visible_ids_.end() ||
+      cache_.size() < cache_.MaximumCacheSize()) {
+    return;
+  }
+
+  TabId key_to_remove;
+  bool found_key_to_remove = false;
+
+  // 1. Find a cached item not in this list
+  for (ExpiringThumbnailCache::iterator iter = cache_.begin();
+       iter != cache_.end();
+       iter++) {
+    if (std::find(visible_ids_.begin(), visible_ids_.end(), iter->first) ==
+        visible_ids_.end()) {
+      key_to_remove = iter->first;
+      found_key_to_remove = true;
+      break;
+    }
+  }
+
+  if (!found_key_to_remove) {
+    // 2. Find the least important id we can remove.
+    for (TabIdList::reverse_iterator riter = visible_ids_.rbegin();
+         riter != visible_ids_.rend();
+         riter++) {
+      if (cache_.Contains(*riter)) {
+        key_to_remove = *riter;
+        break;
+        found_key_to_remove = true;
+      }
+    }
+  }
+
+  if (found_key_to_remove)
+    cache_.Remove(key_to_remove);
+}
+
+void ThumbnailCache::RemoveFromReadQueue(TabId tab_id) {
+  TabIdList::iterator read_iter =
+      std::find(read_queue_.begin(), read_queue_.end(), tab_id);
+  if (read_iter != read_queue_.end())
+    read_queue_.erase(read_iter);
+}
+
+void ThumbnailCache::InvalidateCachedThumbnail(const Thumbnail& thumbnail) {
+  TabId tab_id = thumbnail.tab_id();
+  base::Time time_stamp = thumbnail.time_stamp();
+
+  if (cache_.Contains(tab_id) && cache_.Get(tab_id).time_stamp() == time_stamp)
+    cache_.Remove(tab_id);
+
+  if (approximation_cache_.Contains(tab_id) &&
+      approximation_cache_.Get(tab_id).time_stamp() == time_stamp)
+    approximation_cache_.Remove(tab_id);
+}
+
+base::FilePath ThumbnailCache::GetFilePath(TabId tab_id) const {
+  return disk_cache_path_.Append(base::IntToString(tab_id));
+}
+
+void ThumbnailCache::WriteTask(
+    const base::FilePath& file_path,
+    skia::RefPtr<SkPixelRef> compressed_data,
+    float scale,
+    const gfx::Size& content_size,
+    scoped_refptr<ThumbnailCache::WriteTaskResult> result) {
+  DCHECK(compressed_data);
+  DCHECK(result);
+
+  base::File file(file_path,
+                  base::File::FLAG_CREATE_ALWAYS | base::File::FLAG_WRITE);
+  DCHECK(file.IsValid());
+
+  compressed_data->lockPixels();
+  bool success = true;
+  int content_width = content_size.width();
+  int content_height = content_size.height();
+  int data_width = compressed_data->info().width();
+  int data_height = compressed_data->info().height();
+
+  if (file.WriteAtCurrentPos(reinterpret_cast<const char*>(&kCompressedKey),
+                             sizeof(int)) < 0 ||
+      file.WriteAtCurrentPos(reinterpret_cast<const char*>(&content_width),
+                             sizeof(int)) < 0 ||
+      file.WriteAtCurrentPos(reinterpret_cast<const char*>(&content_height),
+                             sizeof(int)) < 0 ||
+      file.WriteAtCurrentPos(reinterpret_cast<const char*>(&data_width),
+                             sizeof(int)) < 0 ||
+      file.WriteAtCurrentPos(reinterpret_cast<const char*>(&data_height),
+                             sizeof(int)) < 0 ||
+      file.WriteAtCurrentPos(reinterpret_cast<const char*>(&scale),
+                             sizeof(float)) < 0) {
+    success = false;
+  }
+
+  size_t compressed_bytes = etc1_get_encoded_data_size(data_width, data_height);
+  if (file.WriteAtCurrentPos(reinterpret_cast<char*>(compressed_data->pixels()),
+                             compressed_bytes) < 0)
+    success = false;
+
+  compressed_data->unlockPixels();
+
+  if (!success)
+    base::DeleteFile(file_path, false);
+
+  file.Close();

[David Trainor- moved to gerrit, 2014/07/15 20:08:23]

Do you have to close this before you delete the file?  Maybe simulate a failed
write and make sure this works?

[powei, 2014/07/18 00:51:49]

Done.  Moved close to before delete.

+
+  result->SetSuccess(success);
+}
+
+void ThumbnailCache::PostWriteTask(
+    TabId tab_id,
+    scoped_refptr<ThumbnailCache::WriteTaskResult> result) {
+  write_tasks_count_--;
+  if (result->success())
+    written_thumbnails_.insert(tab_id);
+}
+
+void ThumbnailCache::CompressionTask(
+    SkBitmap raw_data,
+    scoped_refptr<ThumbnailCache::CompressedDataTransport> transport) {
+  if (raw_data.empty())
+    return;
+
+  SkAutoLockPixels raw_data_lock(raw_data);
+  gfx::Size raw_data_size(raw_data.width(), raw_data.height());
+  DCHECK_EQ(raw_data.config(), SkBitmap::kARGB_8888_Config);
+  size_t pixel_size = 4;  // Pixel size is 4 bytes for kARGB_8888_Config.
+  size_t stride = pixel_size * raw_data_size.width();
+
+  gfx::Size encoded_size = GetEncodedSize(raw_data_size);
+  size_t encoded_bytes =
+      etc1_get_encoded_data_size(encoded_size.width(), encoded_size.height());
+  SkImageInfo info = {encoded_size.width(),
+                      encoded_size.height(),
+                      kUnknown_SkColorType,
+                      kUnpremul_SkAlphaType};
+  skia::RefPtr<SkData> etc1_pixel_data = skia::AdoptRef(
+      SkData::NewFromMalloc(new uint8_t[encoded_bytes], encoded_bytes));
+  skia::RefPtr<SkMallocPixelRef> etc1_pixel_ref = skia::AdoptRef(
+      SkMallocPixelRef::NewWithData(info, 0, NULL, etc1_pixel_data.get()));
+
+  etc1_pixel_ref->lockPixels();
+  bool success = etc1_encode_image(
+      reinterpret_cast<unsigned char*>(raw_data.getPixels()),
+      raw_data_size.width(),
+      raw_data_size.height(),
+      pixel_size,
+      stride,
+      reinterpret_cast<unsigned char*>(etc1_pixel_ref->pixels()),
+      encoded_size.width(),
+      encoded_size.height());
+  etc1_pixel_ref->setImmutable();
+  etc1_pixel_ref->unlockPixels();
+  if (success) {
+    transport->compressed_data = etc1_pixel_ref;
+    transport->content_size = raw_data_size;
+  }
+}
+
+void ThumbnailCache::PostCompressionTask(
+    TabId tab_id,
+    float scale,
+    const base::Time& time_stamp,
+    scoped_refptr<ThumbnailCache::CompressedDataTransport> transport) {
+  DCHECK(transport);
+  compression_tasks_count_--;
+
+  if (!transport->compressed_data)
+    return;

[David Trainor- moved to gerrit, 2014/07/15 20:08:24]

Do we need to clean anything up here?

[powei, 2014/07/18 00:51:49]

Done.

+
+  if (cache_.Contains(tab_id)) {
+    Thumbnail& thumbnail = cache_.Get(tab_id);
+    if (thumbnail.time_stamp() != time_stamp)
+      return;
+    thumbnail.SetCompressedBitmap(transport->compressed_data,
+                                  transport->content_size);
+    thumbnail.CreateUIResource();
+  }
+  WriteThumbnailIfNecessary(
+      tab_id, transport->compressed_data, scale, transport->content_size);
+}
+
+void ThumbnailCache::ReadTask(
+    const base::FilePath& file_path,
+    scoped_refptr<ThumbnailCache::CompressedDataTransport> transport) {
+  DCHECK(transport);
+  if (!base::PathExists(file_path))
+    return;
+
+  base::File file(file_path, base::File::FLAG_OPEN | base::File::FLAG_READ);
+  DCHECK(file.IsValid());
+
+  int key;
+  bool success = true;
+  if (file.ReadAtCurrentPos(reinterpret_cast<char*>(&key), sizeof(int)) < 0 ||
+      key != kCompressedKey)
+    success = false;
+
+  int width, height;
+  if (file.ReadAtCurrentPos(reinterpret_cast<char*>(&width), sizeof(int)) < 0 ||
+      file.ReadAtCurrentPos(reinterpret_cast<char*>(&height), sizeof(int)) < 0)
+    success = false;
+  gfx::Size content_size(width, height);
+
+  if (file.ReadAtCurrentPos(reinterpret_cast<char*>(&width), sizeof(int)) < 0 ||
+      file.ReadAtCurrentPos(reinterpret_cast<char*>(&height), sizeof(int)) < 0)
+    success = false;
+  gfx::Size data_size(width, height);
+
+  float scale = 0.f;
+  if (file.ReadAtCurrentPos(reinterpret_cast<char*>(&scale), sizeof(float)) < 0)
+    success = false;
+
+  size_t compressed_bytes =
+      etc1_get_encoded_data_size(data_size.width(), data_size.height());
+
+  SkImageInfo info = {data_size.width(),
+                      data_size.height(),
+                      kUnknown_SkColorType,
+                      kUnpremul_SkAlphaType};
+
+  scoped_ptr<uint8_t[]> data(new uint8_t[compressed_bytes]);
+  if (file.ReadAtCurrentPos(reinterpret_cast<char*>(data.get()),
+                            compressed_bytes) < 0)
+    success = false;
+
+  skia::RefPtr<SkData> etc1_pixel_data =
+      skia::AdoptRef(SkData::NewFromMalloc(data.release(), compressed_bytes));
+  skia::RefPtr<SkPixelRef> compressed_data = skia::AdoptRef(
+      SkMallocPixelRef::NewWithData(info, 0, NULL, etc1_pixel_data.get()));
+
+  if (success) {
+    transport->compressed_data = compressed_data;
+    transport->scale = scale;
+    transport->content_size = content_size;
+  } else {
+    base::DeleteFile(file_path, false);
+  }
+
+  file.Close();
+}
+
+void ThumbnailCache::PostReadTask(
+    TabId tab_id,
+    scoped_refptr<ThumbnailCache::CompressedDataTransport> transport) {
+  TabIdList::iterator iter =
+      std::find(read_queue_.begin(), read_queue_.end(), tab_id);
+  if (iter == read_queue_.end())
+    return;
+
+  read_queue_.erase(iter);
+
+  if (!cache_.Contains(tab_id) && transport->compressed_data) {
+    DCHECK(thumbnail_meta_data_.find(tab_id) != thumbnail_meta_data_.end());
+
+    MakeSpaceForNewItemIfNecessary(tab_id);
+    Thumbnail thumbnail(tab_id,
+                        thumbnail_meta_data_[tab_id].capture_time(),
+                        transport->scale,
+                        ui_resource_provider_,
+                        this);
+    thumbnail.SetCompressedBitmap(transport->compressed_data,
+                                  transport->content_size);
+    cache_.Put(tab_id, thumbnail);

[David Trainor- moved to gerrit, 2014/07/14 20:30:46]

thumbnail.CreateUIResource?

[powei, 2014/07/14 23:56:25]

Just to make sure.  This means we prefer cpu mem over video mem?

[powei, 2014/07/15 20:06:09]

Done.

[David Trainor- moved to gerrit, 2014/07/15 20:08:23]

Yes.  At least when it was in Dalvik that was the case.  Maybe add a
flag/constant we can tweak to determine whether or not this happens then we can
run some tests.

[powei, 2014/07/22 18:16:19]

Done.  Forgot the flag in the last patch.  Now added.

+    NotifyObserversOfThumbnailRead(tab_id);
+  }
+
+  ReadNextThumbnail();
+}
+
+void ThumbnailCache::NotifyObserversOfThumbnailRead(TabId tab_id) {
+  FOR_EACH_OBSERVER(
+      ThumbnailCacheObserver, observers_, OnFinishedThumbnailRead(tab_id));
+}
+
+ThumbnailCache::ThumbnailMetaData::ThumbnailMetaData() {
+}
+
+ThumbnailCache::ThumbnailMetaData::ThumbnailMetaData(
+    const base::Time& current_time,
+    const GURL& url)
+    : capture_time_(current_time), url_(url) {
+}
+
+std::pair<SkBitmap, float> ThumbnailCache::CreateApproximation(
+    const SkBitmap& bitmap,
+    float scale) {
+  DCHECK(!bitmap.empty());
+  DCHECK_GT(scale, 0);
+  SkAutoLockPixels bitmap_lock(bitmap);
+  float new_scale = 1.f / kApproximationScaleFactor;
+
+  gfx::Size dst_size = gfx::ToFlooredSize(
+      gfx::ScaleSize(gfx::Size(bitmap.width(), bitmap.height()), new_scale));
+  SkBitmap dst_bitmap;
+  dst_bitmap.setConfig(bitmap.getConfig(), dst_size.width(), dst_size.height());
+  dst_bitmap.allocPixels();
+  dst_bitmap.eraseColor(0);
+  SkAutoLockPixels dst_bitmap_lock(dst_bitmap);
+
+  SkCanvas canvas(dst_bitmap);
+  canvas.scale(new_scale, new_scale);
+  canvas.drawBitmap(bitmap, 0, 0, NULL);
+  dst_bitmap.setImmutable();
+
+  return std::make_pair(dst_bitmap, new_scale * scale);
+}