Remove the concept of pendingScripts from HTMLScriptRunner

Remove the concept of pendingScripts from HTMLScriptRunner

We shouldn't need pendingScripts in ScriptRunner since
we should never be trying to run scripts when we're
not ready to run them.

However this wasn't completely true in the case of imports
there was code to have us break before any start tag after
an <import> was seen, but it was subtly wrong in that it
it would include the start-tag it was trying to break before
in the chunk it sent to the main thread.

This didn't run out to be the problem I was facing, but I fixed
it anyway.  The problem which was actually preventing me from
removing pendingScripts was adding a check inside
didRecieveParsedChunk... to check if imports were pending and
add the chunk to the list of pending chunks.

I also renamed m_speculations to m_pendingChunks since these
chunks are never speculative anymore.

We can't test the off-by-one import-breaking code with our
current system, but it would be trivial to test with a
self-closing custom element if/when we ever add custom
elements back to the system.

R=abarth@chromium.org
BUG=

Committed: https://chromium.googlesource.com/external/mojo/+/699c4cc34b01ea80e125f166374be508d5de3b2c

[abarth-chromium, 2015-02-17 23:58:17]

lgtm

[eseidel, 2015-02-18 00:13:34]

Committed patchset #1 (id:1) manually as
699c4cc34b01ea80e125f166374be508d5de3b2c (presubmit successful).