Changing webmenc to use libwebm

Changing webmenc to use libwebm for WebM file muxing.

Change-Id: I38ccc74f35c6b9684a87d04d8f9354dbe9a3263b
Cleaning up get_sby_perpixel_{, diff_}variance().

Change-Id: Icbfeb04647d654253866d290abd4775a877b4f61
Fix encoder uninitialized read errors reported by drmemory

This patch fixed the uninitialized read errors in Issue 748:
"dr memory VP9 encode errors". In vp9_convolve_avg_sse2,
when width is 4, pavgb reads 8 bytes from dst buffer that is
out of range. An error is reported although the data is not
actually used later. This issue was resolved by preventing
uninitialized reads.

Change-Id: I109a54910aa47139cb13119de86f2062cff207df
Minor code cleanup

Cleanup.

Change-Id: I54d989e24b35323cda7290654e425565d5c9ea2d
Remove duplicate code

Change-Id: Ie26b6ca8de733a527f820b16148e7a2231073f0f
Regrouping code in rd_pick_sb_modes().

Change-Id: I51c71dd4aee6592fb90feebcf864bccc87dacec6
Cleanup table declarations in vp9_rdopt.

Change-Id: Ia4bef41a6b0252593ad84612a2a143c724fd03ea
Fix coding format in vp9_rc_regulate_q

Change-Id: I08aa0c213df34c084eb7a3c51b6b3306e49c7757
Removing unused initial_{width, height} from VP9Decoder.

Change-Id: I039474b34863bc3db9c6cda82485c32826a1b5d1
Prevent the usage of invalid best_mode_index

This commit changed the initialization of best_mode_index to -1 to make
sure it is not mistakenly used for mode masking.

Change-Id: I75b05db51466070dd23c4ee57a4d4b40764dc019
Remove vestiges of large tx sizes in sub8x8 code.

Change-Id: I27015ed57b4c4390cfde3d0eecd82c3e76fd3786
Merge "Minor code cleanup"
Fix onyx_if.c to not to redefine M_LOG2_E if it's already defined.

This fixes warning when compiling libvpx for PNaCl. PNaCl's version
of math.h defines M_LOG2_E.

Change-Id: Iba9450441538e9f82447ad2936bea94d21bafdf1
Merge "Remove duplicate code"
Merge "Prevent the usage of invalid best_mode_index"
Merge "Fix coding format in vp9_rc_regulate_q"
Merge "Fix encoder uninitialized read errors reported by drmemory"
Define var threshold as unsigned int to match the type

Minor change to use matching type in comparison.

Change-Id: I670cae2d584918c67c1af791a797629f392f599e
Merge "Cleanup table declarations in vp9_rdopt."
Merge "Remove vestiges of large tx sizes in sub8x8 code."