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This CL adds support for decoding eh-related wasm opcodes:
* Throw: used for raising an exception; the thrown value lives on top of
         the evaluation stack;
* TryCatch: used to start a try block that has a catch clause;
* TryFinally: used to start a try block that has a finally clause;
* TryCatchFinally: used to start a try block that has both catch and
                   finally clauses;
* Catch <local>: used to start the catch block of a
                 TryCatch/TryCatchFinally block; the thrown value is
                 stored in local <local>; and
* Finally: used to start a finally block of TryFinally/TryCatchFinally.

Three different opcodes are used to start a try block to simplify the
AST construction during bytecode parsing.

BUG=

Review-Url: https://codereview.chromium.org/2222193004
Cr-Commit-Position: refs/heads/master@{#38579}