This reverts commit c13bda86.

Reason for revert: May have broken LibFuzzer and AFL builds:

https://ci.chromium.org/buildbot/chromium.fyi/Afl%20Upload%20Linux%20ASan/7718
https://build.chromium.org/deprecated/chromium.fyi/builders/Libfuzzer%20Upload%20Linux%20ASan/builds/8691

In file included from ../../third_party/angle/src/compiler/translator/TextureFunctionHLSL.cpp:12:
In file included from ../../third_party/angle/src/compiler/translator/TextureFunctionHLSL.h:19:
../../third_party/angle/src/compiler/translator/InfoSink.h:40:16: error: call to function 'operator<<' that is neither visible in the template definition nor found by argument-dependent lookup
        stream << t;
               ^
../../third_party/angle/src/compiler/translator/TextureFunctionHLSL.cpp:111:9: note: in instantiation of function template specialization 'sh::TInfoSinkBase::operator<<<sh::ImmutableString>' requested here
    out << textureReference;
        ^
../../third_party/angle/src/compiler/translator/ImmutableString.h:76:15: note: 'operator<<' should be declared prior to the call site or in namespace 'sh'
std::ostream &operator<<(std::ostream &os, const sh::ImmutableString &str);
              ^
1 error generated.

Bug: chromium:806619

Original change's description:
> Use ImmutableString for HLSL texture references
> 
> This also adds ImmutableStringBuilder class, which can be used to
> build ImmutableStrings in place without extra allocations if the
> maximum length is known in advance.
> 
> BUG=angleproject:2267
> TEST=angle_unittests
> 
> Change-Id: I4dfb78adeb0cffcfad0d25753fb8063466012c92
> Reviewed-on: https://chromium-review.googlesource.com/886362
> Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>
> Reviewed-by: Jamie Madill <jmadill@chromium.org>

TBR=jmadill@chromium.org,cwallez@chromium.org,oetuaho@nvidia.com

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: angleproject:2267
Change-Id: I445f5a786f8b16c3f40f28df09d45fcb215a9c88
Reviewed-on: https://chromium-review.googlesource.com/890542Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>