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Revert of Adding StringPiece read/write support to pickle. (patchset #4 id:60001 of https://codereview.chromium.org/927183002/)

Reason for revert:
Causing crashes on Linux. Investigating.
Bug 464180.

Original issue's description:
> Adding StringPiece/StringPiece16 read/write support to pickle, and
> update unit tests.
>
> The IPC perf tests do a lot of allocations which can, with large block
> sizes, harm their performance. The high allocation counts also make
> their performance very dependent on the quirks of the Windows heap, as
> it applies undocumented heuristics to decide when to decommit memory
> and when to save it for later.
>
> And, doing unnecessary allocations is generally always a bad thing.
>
> So, this change adds StringPiece support to PickleIterator (reading)
> and Pickle (writing). The StringPiece function now handles all strings
> when writing, but must be requested explicitly when reading.
>
> ipc_mojo_perftests does more allocations than ipc_perftests. This
> removes one message-sized allocation from both tests.
>
> The unit tests were updated so that WriteString and WriteString16 are
> exercised with both string objects and char/char16 arrays (no
> allocations required!). Reading into StringPiece and StringPiece16 is
> also tested and the tests were verified with:
> out\Release\base_unittests --gtest_filter=PickleTest.*
>
> The main performance test command line used was:
>
> out\Release\ipc_mojo_perftests --gtest_filter=MojoChannelPerfTest.ChannelPingPong
>
> Typical test results on HP Z620 (Windows 8.1) with thread affinity and
> high-performance power settings prior to this change:
> IPC_Channel_Perf_50000x_12      1140.01 ms
> IPC_Channel_Perf_50000x_144     1182.55 ms
> IPC_Channel_Perf_50000x_1728    1266.42 ms
> IPC_Channel_Perf_12000x_20736   1289.19 ms
> IPC_Channel_Perf_1000x_248832   584.619 ms
>
> Typical test results with same settings but using base::StringPiece:
> IPC_Channel_Perf_50000x_12      1123.33 ms
> IPC_Channel_Perf_50000x_144     1164.53 ms
> IPC_Channel_Perf_50000x_1728    1242.99 ms
> IPC_Channel_Perf_12000x_20736   1186.84 ms
> IPC_Channel_Perf_1000x_248832   496.469 ms
>
> Modest improvement with small buffers, but significant speedup with large buffers.
>
> Typical test results with large-blocks only prior to this change:
> IPC_Channel_Perf_1000x_248832   1211.33 ms
> IPC_Channel_Perf_1000x_248832   961.404 ms
> IPC_Channel_Perf_1000x_248832   600.911 ms
> IPC_Channel_Perf_1000x_248832   468.356 ms
> IPC_Channel_Perf_1000x_248832   430.859 ms
> IPC_Channel_Perf_1000x_248832   425.147 ms
>
> Typical test results with large-blocks only (base::StringPiece):
> IPC_Channel_Perf_1000x_248832   909.571 ms
> IPC_Channel_Perf_1000x_248832   731.435 ms
> IPC_Channel_Perf_1000x_248832   493.697 ms
> IPC_Channel_Perf_1000x_248832   417.966 ms
> IPC_Channel_Perf_1000x_248832   397.377 ms
> IPC_Channel_Perf_1000x_248832   397.725 ms
>
> Note that it takes a while for the Windows heap to 'realize' that it
> should hang on to some of the large blocks which is why performance
> increases over multiple runs.
>
> Chrome will not immediately be affected because StringPiece reading has
> to be explicitly selected. Note that the effect on ipc_perftests is
> more variable due to the odd Windows heap heuristics.
>
> Reliable results require setting the power plan to high-performance.
> On Linux this is done with this command:
> sudo cpupower frequency-set --governor performance
>
> The ipc_perftests command-line is:
> out/Release/ipc_perftests --gtest_filter=IPCChannelPerfTest.ChannelPingPong
>
> Typical before/after Linux results for ipc_perftests are:
> IPC_Channel_Perf_50000x_12      465.271 ms
> IPC_Channel_Perf_50000x_144     480.224 ms
> IPC_Channel_Perf_50000x_1728    510.871 ms
> IPC_Channel_Perf_12000x_20736   318.016 ms
> IPC_Channel_Perf_1000x_248832   309.325 ms
>
> IPC_Channel_Perf_50000x_12      459.245 ms
> IPC_Channel_Perf_50000x_144     479.347 ms
> IPC_Channel_Perf_50000x_1728    506.57  ms
> IPC_Channel_Perf_12000x_20736   289.583 ms
> IPC_Channel_Perf_1000x_248832   255.083 ms
>
> Before after Linux results for ipc_mojo_perftests:
> IPC_Channel_Perf_50000x_12      670.727 ms
> IPC_Channel_Perf_50000x_144     713.6   ms
> IPC_Channel_Perf_50000x_1728    808.157 ms
> IPC_Channel_Perf_12000x_20736   464.221 ms
> IPC_Channel_Perf_1000x_248832   365.258 ms
>
> IPC_Channel_Perf_50000x_12      653.12  ms
> IPC_Channel_Perf_50000x_144     697.418 ms
> IPC_Channel_Perf_50000x_1728    772.575 ms
> IPC_Channel_Perf_12000x_20736   446.315 ms
> IPC_Channel_Perf_1000x_248832   348.38  ms
>
> So, consistent improvements on Linux.
>
> Committed: https://crrev.com/fcfde7d98209569fba81de4f1b26d0e26cd95848
> Cr-Commit-Position: refs/heads/master@{#319128}

TBR=thestig@chromium.org,cpu@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.chromium.org/981853002

Cr-Commit-Position: refs/heads/master@{#319191}