Revert of Do not consolidate data in BMPImageDecoder

Revert of Do not consolidate data in BMPImageDecoder (patchset #9 id:160001 of https://codereview.chromium.org/1259083003/ )

Reason for revert:
crbug.com/530279

This comment [1] describes what needs to be done to reland.

[1] https://code.google.com/p/chromium/issues/detail?id=530279#c1

Original issue's description:
> Do not consolidate data in BMPImageDecoder
> 
> In BMPImageDecoder, never call SharedBuffer::data(), which potentially
> copies all the data. Instead, do the following:
> 
> - Read directly from the SharedBuffer when it is safe to do so. e.g.
>   when only one byte is needed. We already know there is enough data,
>   and getSomeData will return at least a byte if there is enough data.
> - Use a FastSharedBufferReader when we may be on a segment boundary.
> 
> As a result, we make fewer copies when decoding BMPs. We never call
> SharedBuffer::data(), which copies up to the entire encoded data
> received so far. Occasionally we will make small copies when a two or
> four byte number is on a segment boundary.
> 
> Add a setter to FastSharedBufferReader to update its SharedBuffer, so the
> BMPImageReader can have one as a member, which it will reuse across calls.
> 
> Remove BIG_ENDIAN, and eliminate another memcpy that was there to support
> it.
> 
> Using my modified version of ImageDecodeBench (see crrev.com/1145373003),
> I see a slight speedup as compared to the old version which relied on
> SharedBuffer::data(). (My data can be found here: [1].) This matches my
> expectations, since the new version is copying less data.
> 
> Using a version of ImageDecodeBench with a premerged buffer (see
> crrev.com/1318713005), I still see a speed improvement, although it is
> very small. (See sheet 2 of the above spreadsheet).
> 
> [1] https://docs.google.com/a/google.com/spreadsheets/d/1GN2FDytKvkdZzV-WF4IEQaYQF65wa4bRxG67bNgpjAE/edit?usp=sharing
> 
> BUG=467772
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=201811

TBR=noel@chromium.org,pkasting@chromium.org,fmalita@chromium.org,scroggo@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=467772
Committed: https://crrev.com/019c3ffda974f22c79c7d2d4833c0a561bce206f
git-svn-id: svn://svn.chromium.org/blink/trunk@202201 bbb929c8-8fbe-4397-9dbb-9b2b20218538

[scroggo, 2015-09-14 13:30:10]

Created Revert of Do not consolidate data in BMPImageDecoder

[commit-bot: I haz the power, 2015-09-14 13:30:12]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1337263003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1337263003/1

[commit-bot: I haz the power, 2015-09-14 13:30:14]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-09-14 13:30:14]

No L-G-T-M from a valid reviewer yet. Only full committers are accepted.
Even if an L-G-T-M may have been provided, it was from a non-committer,
_not_ a full super star committer.
See http://www.chromium.org/getting-involved/become-a-committer
Note that this has nothing to do with OWNERS files.

[Noel Gordon, 2015-09-14 13:35:59]

LGTM

[Noel Gordon, 2015-09-14 13:36:58]

The CQ bit was checked by noel@chromium.org

[commit-bot: I haz the power, 2015-09-14 13:37:04]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1337263003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1337263003/1

[commit-bot: I haz the power, 2015-09-14 13:37:20]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-09-14 13:37:20]

Failed to apply patch for
Source/platform/image-decoders/FastSharedBufferReader.cpp:
While running patch -p1 --forward --force --no-backup-if-mismatch;
  patching file Source/platform/image-decoders/FastSharedBufferReader.cpp
  Hunk #1 FAILED at 41.
  1 out of 1 hunk FAILED -- saving rejects to file
Source/platform/image-decoders/FastSharedBufferReader.cpp.rej

Patch:       Source/platform/image-decoders/FastSharedBufferReader.cpp
Index: Source/platform/image-decoders/FastSharedBufferReader.cpp
diff --git a/Source/platform/image-decoders/FastSharedBufferReader.cpp
b/Source/platform/image-decoders/FastSharedBufferReader.cpp
index
c4a8107012523bc5da80c7fcd7102378e31d11c3..3eac7cf1844447158d1351a97bc5d3e01b975128
100644
--- a/Source/platform/image-decoders/FastSharedBufferReader.cpp
+++ b/Source/platform/image-decoders/FastSharedBufferReader.cpp
@@ -41,16 +41,6 @@
 {
 }
 
-void FastSharedBufferReader::setData(PassRefPtr<SharedBuffer> data)
-{
-    if (data == m_data)
-        return;
-    m_data = data;
-    m_segment = 0;
-    m_segmentLength = 0;
-    m_dataPosition = 0;
-}
-
 const char* FastSharedBufferReader::getConsecutiveData(size_t dataPosition,
size_t length, char* buffer)
 {
     RELEASE_ASSERT(dataPosition + length <= m_data->size());

[scroggo, 2015-09-14 14:03:58]

The CQ bit was checked by scroggo@google.com

[scroggo, 2015-09-14 14:03:59]

The patchset sent to the CQ was uploaded after l-g-t-m from noel@chromium.org
Link to the patchset: https://codereview.chromium.org/1337263003/#ps170001
(title: "Rebase")

[commit-bot: I haz the power, 2015-09-14 14:04:04]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1337263003/170001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1337263003/170001

[commit-bot: I haz the power, 2015-09-14 14:04:28]

Committed patchset #2 (id:170001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=202201

[Peter Kasting, 2015-09-14 19:43:20]

LGTM.  FYI, I don't have visibility of that bug.

[commit-bot: I haz the power, 2015-09-23 12:32:09]

Patchset 2 (id:??) landed as
https://crrev.com/019c3ffda974f22c79c7d2d4833c0a561bce206f