LSC: Add namespace qualifiers to global names.
LSC: Add namespace qualifiers to global names.

This large-scale change (go/global-namespace-lsc) updates references to several
common global names in google3 to instead use their namespace-qualified
equivalents. Uses of the global names typically rely on C++ unqualified name
lookup rules, which includes Argument-Dependent Lookup. Changes to move google3
to C++17 will substantially increase the likelihood of lookups accidentally
invoking ADL, which may make code more brittle, or may break it entirely, in
mysterious ways. Changing lookups to use qualified names instead avoids the
issue of ADL altogether (note also that the qualified names are already
preferred by the C++ style guide).

This is an omnibus change of several notionally separate cleanups. The common
thread is that they move functions out of the global namespace, which will
become increasingly painful as google3 moves to C++17.

Summary of changes:
 - Several global aliases for std:: names are being replaced with their
   qualified equivalent. (See: https://goto.google.com/wbysc, note that this
   does not include std::string.)
 - Code in net/base and net/util is moving into the net_base:: and net_util::
   namespaces, respectively. References are updated accordingly.
 - The IPAddress class is moving from net/util to net/base, and into the
   net_base:: namespace. References are updated accordingly.
 - References to code under util/gtl are updated to use the names in the gtl::
   namespace.
 - Some code is moving from third_party/absl/strings back to strings. References
   are updated to use the strings:: namespace and headers.
 - To avoid spurious churn, changes that would otherwise be part of
   go/lsc-absl-gplc are included. In many cases, applying these changes
   independently would cause formatting churn.

More information: go/global-namespace-lsc

Tested:
    TAP sample presubmit queue
    http://test/OCL:190176224:BASE:190415458:1522039576831:34433578

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=190531340

GoogleCloudPlatform/cloud-debug-java,GoogleCloudPlatform/cloud-debug-java,GoogleCloudPlatform/cloud-debug-java,GoogleCloudPlatform/cloud-debug-java